NUREG-2128

Spurious Operation

HS/SO Possible

100%

28%

72%

33%

80%

20%

37%

63%

55%

0

10

20

30

40

50

60

70

80

90

Data Set

q1

min

median

max

q3

maximum

lower

quartile

upper

quartile

25th

percentile

50th percentile

75th

percentile

1-7

box plots only account for conductors that are associated with an end device which actually

spurious operated.

Box plots show a measure of central location (median), two measures of dispersion (the

interquartile range, defined as the difference between the first and third quartiles), the skew, and

potential outliers. Box plots do this by using the minimum and maximum values, along with the

first, second, and third quartiles of the data set. Quartiles are related to percentiles in that the

first quartile (designated q1) is the 25th percentile. The second quartile (q2) is the 50th

percentile, and is also referred to as the median. The third quartile (q3) is the 75th percentile of

the data. It should be noted that no distributions are assumed in presenting data using box

plots.

The box plots identify the minimum and maximum values in the data set. Lines from these two

points are referred to as the whiskers, and connect to the boxes’ limits. The boxes’ lower and

upper limits indicate the first and third quartiles, respectively. The median is located within the

box and is a reference point for identifying any skewness in the data set. As a general rule, any

whisker which is three times longer than the length of the box most likely indicates an outlier.

As you will see in the test result sections below, the duration data has several long duration

outliers that make it difficult to interpret any variations of the core data. Rather than remove

these long duration data points, the authors have reduced the plot ranges (y-axis) to provide a

better representation of the data variations, with the maximum values designated at the top of

the plot. Tables are included with these box plots to provide all of the information numerically, in

tabular form.

There are numerous methods for calculating quartiles. For simplicity, the authors chose to use

the built-in “quartile” function of Microsoft Excel. Excel uses the following equations to calculate

quartiles:

ݕ ൌ ሺ1െ݃ሻ ∗ ݔሺ݆൅1ሻ ൅ ݃ ∗ ݔሺ݆ ൅ 2ሻ (Equation 1-1)

ሺ݊െ1ሻ ∗݌ൌ݆൅݃ (Equation 1-2)

Where

n = number of values

y = observation number (when values are arranged in ascending order)

p = percentile

j = integer

g = decimal

x() = specific value in ascending list

These equations can be simplified into the following form for the first, second, and third

quartiles:

 1st quartile (q1): ¼*(n+3)th observation

 2nd quartile (median): ½*(n+1) th observation

 3rd quartile (q3): ¼*(3*n+1)th observation.

1-8

1.4 Report Organization

Section 2 presents the AC data taken from the NEI/EPRI, CAROLFIRE, and DESIREE-FIRE

testing projects, evaluating the various intra-cable failure parameters where data was available.

A summary of the systematic parameter evaluation is presented in the latter portion of Section

2, along with evaluations of the effects of suppression and hot short concurrence.

Section 3 provides a review of inter-cable failures observed during testing and the authors’

identification of any influencing parameters. This discussion identifies what was done in the

EPRI and NRC testing programs to provide tests that could be used to evaluate the likelihood of

inter-cable fire-induced hot shorts of AC circuits.

Section 4 presents the DC data taken from the DESIREE-FIRE testing project, evaluating the

various intra-cable failure parameters. This analysis complements the information from Section

2 on the AC data, but also evaluates several additional parameters. This section also includes

a summary of the systematic evaluation of the DC data, along with a review of concurrent hot

shorts that occurred in the intermediate-scale testing of DC circuits.

Section 5 provides a summary of test data related to inter-cable interactions for AC circuits,

similar to what was done in Section 3. The larger portion of Section 5 involves the evaluation of

what is being called “ground equivalent hot shorts,” where multiple cables experience hot

shorts.

Section 6 provides a summary of findings for the entire report.

Section 7 contains the report conclusions.

Section 8 provides references.

Appendix A contains data on the penlight ground fault equivalent inter-cable failure mode

evaluation.

Appendix B contains supplemental information for the CAROLFIRE reports, including additional

data retrieval.

2-1

2. INTRA-CABLE – ALTERNATING CURRENT CIRCUITS

2.1 AC Data Analysis Approach

An alternating current (AC) motor-operated valve (MOV) circuit was the primary circuit used in

the NEI/EPRI and Cable Response to Live Fire (CAROLFIRE) testing projects to evaluate the

likelihood of spurious operations. A small set of tests in the Direct Current Electrical Shorting in

Response to Exposure Fire (DESIREE-FIRE) project also used the AC MOV circuitry. The AC

MOV circuit typically had passive targets representing indicating lamps, two active targets

(forward and reverse motor starter contactor), spare conductors, one to two energized (source)

conductors, and at least one common return.

The definition of a hot short is important to this work. As stated previously, only a hot short that

is of sufficient quality to actuate the end device is of interest. Thus, low-quality hot shorts that

would not cause the circuit to respond would not be of interest. Therefore, threshold values are

defined as identifying the energy levels (voltage or current) that would be required to cause the

active and passive targets to change state. This information is presented in Table 2-1,

identifying the failure threshold values for the AC MOV circuit. Active targets are considered to

be those cable conductors which are connected to one of the two MOV contactors. If these

active target conductors become energized during fire-induced cable failure with sufficient

voltage and current, the contactors will pull in, and, in real plant systems, the motor will become

energized to move in either the open or close direction, depending upon which contactor

becomes energized. For the AC test data, a hot short on a passive target or on a spare

conductor was counted when that electrical conductor achieved a voltage level of 80V. The

choice of 80V is based on the authors’ judgment and discussion with the Phenomena

Identification and Ranking Table (PIRT) panel. For an indication lamp, 80V is sufficient to

illuminate the lamp, and for an ungrounded spare the 80V threshold was thought to be sufficient

to eliminate the likelihood that the measurement would derive from induced voltages on the

spare conductor.

Table 2-1. AC threshold values used for MOV hot short & spurious operation

determinations

NEI/EPRI CAROLFIRE DESIREE-FIRE

Active Targets Pick-up Voltage 80V 72V 80V

Drop-out Voltage 60V 65V 60V

Passive Targets Voltage 80V 80V 80V

Spare Voltage 100V 100V 100V

For continuous hot shorts, the duration time was calculated from the start of a hot short to the

end, which was typically a fuse clear. In several cases, a circuit will experience several

successive hot shorts on the same conductor. In these cases, the duration is based on the sum

of the individual durations. For example, assume that conductor number three of circuit A

experienced three hot shorts lasting 10, 15, and 5 seconds respectively; the duration reported

would be 30 seconds, based on the authors’ judgment and discussions among the PIRT panel.

This is considered to be a conservative approach, but also realistic for components, such as a

motor-operated valve, that would not return to their original state following the clearing of the hot

short/spurious operation, requiring a finite stroke time to open or close.

2-2

Once all of the information from the tests was entered into the spreadsheet, the data was

reviewed for circuit configurations that fell outside of the majority of the test data. These outlier

circuit configurations were removed from further use in the study. For instance, in CAROLFIRE,

there were several tests that were designed to evaluate the likelihood of inter-cable shorting.

Since this analysis is only concerned with intra-cable interactions, the inter-cable data was

removed from this analysis, but is used in Section 3 to evaluate inter-cable hot shorting. In

some of the CAROLFIRE and several of the NEI/EPRI tests, the cables did not fail. In the

cases where the cables are not driven to thermal failure, there is no information on the failure

modes to be learned. Thus, the test circuits that did not fail were removed from further use in

this study.

The final type of data points that were removed from the spreadsheet were instances where the

circuit was instrumented in such a way that it was impossible for the electrical protective device

(fuse) to clear or configure, so that the only method that would allow a fuse clear would be a

short to an external ground. The majority of these cases are from the DESIREE-FIRE testing,

where a flame-retardant Kerite™ (FR-Kerite) cable was tested using AC diagnostics to evaluate

the thermal failure temperature. Here, only source conductors and active target conductors

were included in the test cables. As such, there were no common return paths within the cable

that would cause a fuse clear, which could only occur when an energized conductor came in

contact with a ground plane at low resistance. Although configurations in the plants may exist

when there is no common power source return in a cable with sources and targets, the authors

believed that this data would skew the results, especially for hot short likelihood and duration.

As such, these data points were removed, and were not used in this study.

The last point to make clear is the manner in which the data is presented in the report.

Specifically, there are several ways to present the fault mode data in terms of counting hot

shorts. The discussion that follows provides clarification on the methods that were used in this

report.

Figure 2-1 is a schematic of the surrogate circuit diagnostic unit (SCDU) used in CAROLFIRE to

represent an AC MOV motor starter circuit. Similar circuits were used in the NEI/EPRI and

DESIREE-FIRE testing projects. In Figure 2-1, there are two energized source conductors,

shown as circuit paths 1 and 2. A resistor used to represent an indication lamp is considered to

be a passive target (PT), and is connected to circuit path 4. Circuit paths 5 and 6 are connected

to the forward and reverse motor starter contactors, “K1” and “K2.” These two paths are

considered active targets (AT). Circuit path 7 is connected to the common power supply return,

and circuit path 8 is considered to be an ungrounded spare conductor.

2-3

Figure 2-1. CAROLFIRE AC MOV circuit

Table 2-2 provides information pertaining to the circuit path configuration for the CAROLFIRE

AC MOV SCDU. As shown, paths 5 and 6 can experience both hot shorts and spurious

operations. Circuit Paths 4 and 8 can experience a hot short only.

Table 2-2. CAROLFIRE AC MOV circuit path configuration

Source Hot Short Spurious Operation

Power Supply

Common Return

Circuit Path 1 X

Circuit Path 2 X

Circuit Path 4 X

Circuit Path 5 X X

Circuit Path 6 X X

Circuit Path 7 X

Circuit Path 8 X

Using the global approach, there can only be one of two outcomes: (1) the cable experiences

hot short(s), or (2) the cable experiences a ground fault (clearing of the circuit fuse). Note that

spurious operations are a subset of hot shorts. The global approach does not provide an

indication on the number of hot shorts that occur within a multi-conductor cable; either it occurs,

or it doesn’t. This method does not make any distinction between the numbers of hot shorts.

From these examples, it is important to note that there will always be at least as many hot

shorts as spurious operations. This is because every spurious operation is classified as a hot

short, but not every hot short is classified as a spurious operation.

2-4

For example, let’s assume that the AC MOV circuit shown in Figure 2-1 is used in a test, and

that the following failure modes occurred in this case:

 @ 954 seconds – circuit path 4 experienced a hot short

 @ 1005 seconds – circuit path 6 experienced a hot short

 @ 1013 seconds – circuit path 6 experienced a hot short

 @ 1020 seconds – the circuit fuse cleared

In this example, using the global approach to counting hot shorts and spurious operations, there

was one hot short, one spurious operation, and no fuse clears. In reality there were three hot

shorts, two spurious operations, and one fuse clear. Again, the global approach looks at the

circuit failure modes in a binary fashion. This point is important for understanding the

information that follows in this section and in Section 4.

With regard to calculating duration of the hot shorts and hot short induced spurious operations,

more information is required to calculate the duration using the method outlined above. Using

the previous example, the duration of the hot short and spurious operation is presented using

the following information:

 circuit path 4, hot shorts as follows;

o 954 seconds – hot short starts

o 1020 seconds - hot short ends

 circuit path 6 experienced a hot short induced spurious operation as follows;

o 1005 seconds - spurious operation begins

o 1010 seconds - spurious operation ends

o 1013 seconds - spurious operation begins

o 1020 seconds - spurious operation ends

For circuit path 4, since only one fire-induced hot short occurred, the duration is calculated as

the hot short end time (1020s) minus the hot short start time (954s) resulting a hot short

duration of 66 seconds. For circuit path 6, multiple hot short-induced spurious operations occur

on the same end device. Here the duration is calculated for each individual spurious operation

and all of the individual durations are summed together to arrive at a total duration for circuit

path 6. This is shown in Equation 2-1.

Circuit Path 6 duration: (1010 s – 1005 s) + (1020 s – 1013 s) = 12 seconds Equation 2-1

The last point to make regarding the analysis of the AC test data is that some of CAROLFIRE

and DESIREE-FIRE tests also employed SNL’s patented Insulation Resistance Measurement

System (IRMS), which was operated using AC power. This system provides measurements of

a monitored electrical cable’s insulation resistance as a function of time during fire-induced

cable failure. The IRMS can provide detailed information as to how the individual conductors

are failing; however, it does not represent any type of electrical circuit used in a nuclear power

plant. Several concepts regarding the use of the IRMS data to evaluate failure modes were

discussed during the electrical expert PIRT meetings, but none were technically accurate

enough to be used to supplement the data analysis documented here.

The remainder of this section presents the AC test data evaluated by the various parameters

outlined earlier. Each parameter discusses how the data was binned and then presents the

failure mode likelihood, followed by information on the hot short duration.

2-5

2.2 Conductor Count

The effects of the conductor count on failure modes are evaluated here. The test data included

multi-conductor cables with 3, 5, 6, 7, 8, and 9 conductors. The PIRT members suggested that

the conductor count bins be labeled “1/C,” “2-6/C,” “7-9/C,” “10-15/C,” and “Greater than 15/C.”

Table 2-3 provides the failure mode likelihood data, separated into conductor count ranges.

There is no data publically available for 1/C cables, or for cables with conductor counts greater

than 10/C.

Table 2-3. Conductor count, global approach, AC tests

Global Approach 1/C 2-6/C 7-9/C 10-15/C >15/C

Fuse Clear - 4 41 - -

Hot Short - 2 65 - -

Spurious Operation - 2 56 - -

HS/SO Possible - 6 106 - -

Figure 2-2 presents the information from the above tables in column format. These figures

show that a large portion of data has been collected in the 7-9 conductor range, making it

difficult to assess the influence that conductor count has on hot short and spurious operation

likelihood.

Figure 2-2. Conductor count column plot, global approach, AC tests

Table 2-4 presents data related to the durations of hot shorts and spurious operations, divided

into the same conductor count ranges used above. Figure 2-3 presents this data visually, in a

box plot. Again, the sparse data limits the amount of information that can be obtained relating to

the influence of conductor count on hot short and spurious operation likelihood.

1/C 2-6/C 7-9/C 10-15/C >15/C

Count

0

20

40

60

80

100

120

140

Fuse Clear

Spurious Operation

HS/SO Possible

100%

53%

61%

39%

100%

67%

33%

2-6

Table 2-4. Conductor count, duration data, AC tests

Hot Short Spurious Operation

1/C 2-6/C 7-9/C 10-15/C >15/C 1/C 2-6/C 7-9/C 10-15/C >15/C

q1 - 3 8 - - - 4 10 - -

min - 1 1 - - - 1 1 - -

median - 6 27 - - - 8 33 - -

max - 15 1345 - - - 15 456 - -

q3 - 10 79 - - - 11 81 - -

mean - 7 69 - - - 8 61 - -

Figure 2-3. Conductor count box plot, duration, AC tests

2.3 Thermal Exposure Conditions

The test data used to evaluate the thermal exposure parameter is separated into four general

exposure conditions, radiant, flame, plume, and hot gas layer (HGL). Figure 2-4 shows the

intermediate-scale testing rig used in the CAROLFIRE and DESIREE-FIRE testing projects. It

is important to note that the locations were identified differently in the two testing projects, and

that the lower exterior HGL locations in the CAROLFIRE project (i.e., B and D) were not used in

the DESIREE-FIRE testing project. Care was taken during the analysis to ensure that the

naming conventions did not cause the different exposure locations to be combined within the

same bin.

Flame exposures were considered to be any electrically monitored cable in location A. In

addition, if location A was filled with cables to provide a fuel source during an experiment, the

locations directly above location A (C for CAROLFIRE and B for DESIREE-FIRE) would also be

considered flame exposure locations. Plume exposure locations were considered to be

locations C and F in CAROLFIRE and locations B and D in DESIREE-FIRE unless designated

as flame locations, as discussed previously. HGLs were considered to be those locations

outside of the flame and plume locations. Therefore, HGL exposure bins included locations B,

D, E, and G for CAROLFIRE, and locations C and E for DESIREE-FIRE. In addition, the

penlight exposure provided a radiated thermal exposure to the cables, and all of the Penlight

0

25

50

75

100

1/C 2‐6/C 7‐9/C 10‐15/C >15/C 1/C 2‐6/C 7‐9/C 10‐15/C >15/C

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

1345s 456s

2-7

data is separated into an individual bin labeled “radiant.” The exposure conditions classification

used in the EPRI test report were adopted as reported.

CAROLFIRE DESIREE-FIRE

Figure 2-4. Intermediate-scale cable raceway location

Table 2-5 and Figure 2-5 present the ground fault, hot short, and spurious operation data. This

data shows some deviations between thermal exposure conditions with regard to ground faults,

hot shorts, or spurious operations. Here the flame region has a lower likelihood of experiencing

a fuse clear fault and a higher likelihood of experiencing hot shorts and spurious operations.

The limited number of AC circuit radiant energy tests (five in total) are all from the AC tests

conducted during the DESIREE-FIRE project. Three of these cable samples were of the FRKerite variety, and the remaining two samples were cross-linked polyethylene (XLPE)-insulated.

Table 2-5. Thermal exposure conditions, global approach, AC tests

Global Approach Flame Plume HGL Radiant

Fuse Clear 7 15 19 4

Hot Short 18 22 26 1

Spurious Operation 17 17 23 1

HS/SO Possible 25 37 45 5

2-8

Figure 2-5. Thermal exposure conditions column plot, global approach, AC tests

Table 2-6 and Figure 2-6 present the duration data, separated by thermal exposure conditions

of flame, plume, and HGL exposures. The box and whisker plot shows that there may be a

correlation between hot short/spurious operation duration and thermal exposure conditions. For

flame exposures, the durations are very short, lasting between 1 and 32 seconds. The plume

thermal exposure conditions have durations with a slightly longer and wider range of 6 to 120

seconds4

. The hot gas layer thermal exposures have the largest range of duration, running from

1 to 456 seconds.

This observation is consistent with the physical response of the cables to these exposure

conditions. In a flame impingement exposure, there is a very intense thermal insult on the

cables and the insulation degrades rapidly, thus progressing from the onset of electrical failure

to final circuit failures (fuse clear) in a short time frame. As the exposure conditions become

less intense (i.e., plume then HGL exposures), the degradation of the conductor insulation is

slower and the failures do not cascade to full failure as rapidly.

Table 2-6. Thermal exposure conditions, duration data, AC tests

Hot Short Spurious Operation

Flame Plume HGL Radiant Flame Plume HGL Radiant

q1 2.3 17.5 20.7 0.6 4.2 24 28.9 0.6

min 0.2 5.8 0.4 0.6 0.2 6 0.8 0.6

median 7.3 45.6 78.8 0.6 8 47.4 78.8 0.6

max 31.6 1345 456 0.6 31.6 126 456 0.6

q3 20 72 169.7 0.6 24.6 60 120.7 0.6

mean 11.1 80.6 106.6 0.6 12.7 51.1 103.4 0.6

4

Note that one duration for the hot short plume data set was 1345 seconds. This data point has been removed from the

generalized discussion, but is important when considering maximum test data durations.

Flame Plume HGL Radiant

Count

0

10

20

30

40

50

60

Fuse Clear

Spurious Operation

HS/SO Possible

100%

46%

59%

41%

100%

72%

68%

28%

100%

51%

58%

42%

100%

20%

80%

2-9

Figure 2-6. Thermal exposure conditions box plot, duration, AC tests

2.4 Cable Orientation

Available test data consists of cable arrangement in the vertical and horizontal orientations.

However, only one test project (NEI/EPRI) included testing cables in the vertical orientation, and

the majority of the test data is for cables oriented horizontally. As such, there is too little

information on fire-induced cable failures in the vertical orientation to allow for comparisons.

Table 2-7 and Figure 2-7 present the data, which is separated by cable orientation.

Table 2-7. Cable orientation, global approach, AC tests

Global Approach Horizontal Vertical Total

Fuse Clear 42 3 45

Hot Short 65 2 67

Spurious Operation 56 2 58

HS/SO Possible 107 5 112

0

50

100

150

200

Flame Plume HGL Radiant Flame Plume HGL Radiant

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

1345s 456s 456s

2-10

Figure 2-7. Cable orientation column plot, global approach, AC tests

Table 2-8 and Figure 2-8 present the duration information based on cable orientation binning.

Again, the minimal amount of data in the vertical position inhibits an evaluation of how cable

orientation affects hot short duration.

Table 2-8. Cable orientation, duration data, AC tests

Hot Short Spurious Operation

Horizontal Vertical Horizontal Vertical

q1 7 11 10 12

min 1 6 1 6

median 27 15 32 18

max 1345 120 456 120

q3 77 44 79 69

mean 69 39 60 48

Horizontal Vertical

Count

0

20

40

60

80

100

120

140

Fuse Clear

Spurious Operation

HS/SO Possible

100%

39%

61%

52%

60%

40%

2-11

Figure 2-8. Cable orientation box plot, duration, AC tests

2.5 Raceway Routing

Open ladder-back cable trays, rigid steel conduits, and air drop configurations were all used

during testing. However, the use of cable trays was predominant, and the lack of sufficient data

in the air drop and conduit configurations makes it difficult to determine the effects of raceway

routing type on fire-induced circuit failures. In addition, no data is available for cable trays with

solid bottom covers or vented covers. Table 2-9 and Figure 2-9 present the test data separated

by raceway routing configurations and air, conduit, and tray configurations.

Table 2-9. Raceway routing, global approach, AC tests

Global Approach Air Conduit Tray

Fuse Clear 0 2 43

Hot Short 2 2 63

Spurious Operation 2 2 54

HS/SO Possible 2 4 106

0

50

100

150

Horizontal Vertical Horizontal Vertical

Hot Short SpuriuosOperation

Seconds

q1

min

median

max

q3

1345s 456s

2-12

Figure 2-9. Raceway routing column plot, global approach, AC tests

Table 2-10 and Figure 2-10 present the duration data separated by raceway routing

configurations. This information indicates that air drop tests last longer than configurations

using conduit or cable tray raceways. This observation is likely the result of the ground plane’s

influence on the circuit’s ability to clear fuses. In an air drop test configuration, there is typically

only one conductor that can cause a circuit to experience a fuse clear. This is a common power

supply return (the neutral from the power supply), and it is typically grounded. For a circuit to

clear its protective fusing, a source conductor is required to come in contact with a common

ground. In conduit and cable tray configurations, a more substantial ground plane exists for

source conductors to contact during cable failure. Thus, the lack of ground plane is likely the

cause of the longer durations in the air drop configurations. The effects of gravity, cable type,

and cable clamps/ties may also affect the failure modes among horizontal and vertical

configurations. Although this hypothesis seems reasonable, it should be stated that the air drop

and conduit data are scarce and additional data points may help reinforce this hypothesis.

Table 2-10. Raceway routing, duration data, AC tests

Hot Short Spurious Operation

Air Conduit Tray Air Conduit Tray

q1 79 18 7 179 46 9

min 28 3 1 34 23 1

median 247 48 24 261 75 30

max 320 126 1345 296 126 456

q3 295 86 65 295 100 62

mean 195 56 62 213 75 53

Air Conduit Tray

Count

0

20

40

60

80

100

120

140

Fuse Clear

Spurious Operation

HS/SO Possible

100%

0%

100%

50%

41%

59%

51%

2-13

Figure 2-10. Raceway routing box plot, duration, AC tests

2.6 Raceway Fill

Numerous cable raceway fill configurations were used during testing. To sort the data, three

configuration groups were selected based on the testing configurations, namely bundles,

intermediate fill, and single cable fill. Figure 2-11, Figure 2-12, and Figure 2-13 provide

illustrations of the bundles, intermediate and single cable fill, respectively. Note that no tests

involved cable trays or conduits filled to their maximum loading per the national electric code

(NEC – NFPA 70). Even though the NEI/EPRI test configurations used a 7/c cable surrounded

by three single conductors, that configuration has not been considered a bundle in this work, as

it was loaded into cable trays with numerous other fill cables, as shown in Figure 2-12 and

Figure 2-13.

Figure 2-11. Cable bundle arrangements (3-, 4-, 6-, & 12-cable bundles)

Figure 2-12. Cable tray fill intermediate

0

50

100

150

200

250

300

350

AIR CONDUIT TRAY AIR CONDUIT TRAY

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

1345s 456s

2-14

Figure 2-13. Single layer cable fill

Table 2-11 and Figure 2-14 present the failure mode data binned by raceway fill. One

observation from this data is that the bundle data deviate from the intermediate and single cable

arrangement in both ground faults and hot short/spurious operation occurrences. The data

shows that the occurrence of a ground fault is roughly twice as likely (~52-53%) for the

intermediate and single cable configurations as it is for a bundle configuration (~26%). The

lower likelihood of a ground fault has a dependent effect on the occurrence of a hot short or

spurious operation in the bundle configurations versus the other two configurations. One

possibility is that the bundle configurations typically involve electrical cables at the top of the

cable bundle and are shielded from the cable tray by fill cables that are not monitored for

electrical response. Thus, for grounded circuits, which make up the majority of the test data,

there is a barrier between the electrically monitored cable and the cable tray/conduit, thus

reducing the ground plane influence and decreasing the likelihood of a ground fault. Again, the

ground plane may influence failure mode likelihoods.

Table 2-11. Raceway fill, global approach, AC tests

Global Approach Bundle Intermediate Single

Fuse Clear 13 16 16

Hot Short 37 14 15

Spurious Operation 35 11 11

HS/SO Possible 50 30 31

Figure 2-14. Raceway fill column plot, global approach, AC tests

Bundle Intermediate Single

Count

0

20

40

60

Fuse Clear

Spurious Operation

HS/SO Possible

100%

74%

70%

26%

53%

47%

37%

52%

48%

35%

2-15

Table 2-12 and Figure 2-15 present the hot short and spurious operation duration data

separated by raceway fill categories (bundle, intermediate, and single). From this data, there is

some indication that the intermediate fill duration data differs from that of the other two

configurations; however, the reasoning behind this observation is unclear. One possibility is

that the fill cables act as a heat sink and/or shield for the target cables from the thermal

exposure, thus lowering the thermal exposure condition for the electrically monitored cables.

Table 2-12. Raceway fill, duration data, AC tests

Hot Short Spurious Operation

Bundle Intermediate Single Bundle Intermediate Single

q1 7 18 11 8 24 7

min 1 1 1 1 1 1

median 25 54 21 30 57 21

max 453 1345 198 296 456 198

q3 62 120 63 62 111 75

mean 56 126 43 51 95 51

Figure 2-15. Raceway fill box plot, duration, AC tests

2.7 Insulation Type

The insulation type parameter separates insulation materials into two polymer types, thermoset

(TS) and thermoplastic (TP). Table 2-13 provides a breakdown of how insulation materials were

classified by insulation type. Section 2.8 of this report provides a comparison of failure

characteristics based on insulation materials. Table 2-14 and Figure 2-16 present the test data

separated by cable conductor insulation type, TS and TP. A comparison of the failure modes

between the TS and TP data sets indicate that there is no substantial difference in fuse clear,

hot short, or spurious operations.

0

100

200

300

Bundle Intermediate Single Bundle Intermediate Single

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

2-16

Table 2-13. Breakdown of insulation material by type, AC tests

Thermoset Materials (TS) Thermoplastic Materials (TP)

EPR – ethylene propylene rubber PE – polyethylene

FR-Kerite – Flame Retardant Kerite™ PVC – polyvinyl chloride

SR – Silicone Rubber TEF – Tefzel

SR-V – Silicone Rubber Vitalink™

XLPE – cross-linked polyethylene

XLPO – cross-linked polyolefin

Table 2-14. Insulation type, global approach, AC tests

Global Approach TP TS

Fuse Clear 17 28

Hot Short 22 45

Spurious Operation 20 38

HS/SO Possible 39 73

Figure 2-16. Insulation type column plot, global approach, AC tests

Table 2-15 and Figure 2-17 present the duration data for test configurations segregated by

cable conductor insulation type. Although the mean duration times are slightly higher for TP

materials (73-80 seconds) than for TS materials (53-61 seconds), the inter-quartile range for the

data presented in the box and whisker plot in Figure 2-17 shows no trend between TS and TP

insulation types.

Table 2-15. Insulation type, duration data, AC tests

Hot Short Spurious Operation

TP TS TP TS

q1 5 11 6 15

min 1 1 1 1

median 23 28 24 39

max 456 1345 456 231

q3 100 72 64 81

mean 80 61 73 53

TP TS

Count

0

20

40

60

80

Fuse Clear

Spurious Operation

HS/SO Possible

100%

44%

56% 51%

38%

62%

52%

2-17

Figure 2-17. Insulation type box plot, duration, AC tests

2.8 Insulation Material

In the previous section, the data was segregated by insulation type. In this section, the data

expanded to insulation type classifications to show how insulation materials differ. Table 2-16

and Figure 2-18 present the ground fault, hot short, and spurious operation data segregated by

cable conductor insulation material.

Table 2-16. Insulation material, global approach, AC tests

TS TP

EPR XLPE SR FR-Kerite PE PVC TEF

Fuse Clear 11 11 3 2 9 4 4

Hot Short 23 19 1 1 9 9 4

Spurious Operation 16 19 1 1 7 9 4

HS/SO Possible 34 30 4 3 18 13 8

0

50

100

150

TP TS TP TS

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

456s 1345s 456s 231s

2-18

Figure 2-18. Insulation material column plot, global approach, AC tests

As shown in the figures above, there is minimal data for silicone rubber (SR) and FR-Kerite.

Thus, interpreting the results is difficult, and it will not be attempted here. Figure 2-18 indicates

that the ethylene propylene rubber (EPR) material differs from the others in that there is a

relatively larger gap between hot shorts and spurious operations (about 20%). The other

materials show a nearly unified correlation between hot short and spurious operations based on

the global analysis approach. Over 50% of the EPR data comes from the NEI/EPRI test set,

and that test set-up may influence these results. However, the direct reasoning behind this

difference is unclear to the authors. A comparison of the remaining cable conductor insulation

materials shows similar results related to ground fault, hot short, and spurious operation

likelihoods.

Table 2-17, Table 2-18, and Figure 2-19 present the duration data segregated by cable

insulation material. Note that SR and FR-Kerite have been removed due to a lack of data. One

interesting aspect of this duration data is the small inter-quartile range for polyvinyl chloride

(PVC)-insulated conductors versus the other two TP cable types, polyethylene (PE) and

Tefzel™ (TEF). Both PE and TEF insulation materials show the longest average durations,

which was reflected in the previous section. However, PVC insulation materials have a very

short duration.

Table 2-17. Insulation material hot short only, duration data, AC tests

TS TP

EPR XLPE PE PVC TEF

q1 12 11 18 1 33

min 1 1 1 1 8

median 60 30 55 4 168

max 324 1345 453 32 456

q3 90 49 233 10 203

mean 64 65 117 8 158

EPR XLPE SR FR-Kerite PE PVC TEF

Count

0

10

20

30

40

Fuse Clear

Spurious Operation

HS/SO Possible

100%

68%

47%

32%

37%

63%

75%

25%

67%

33%

50%

39%

50%

31%

69%

50%

2-19

Table 2-18. Insulation material spurious operation only, duration data, AC tests

TS TP

EPR XLPE PE PVC TEF

q1 12 19 27 1 33

min 2 1 3 1 10

median 62 38 55 6 126

max 198 231 296 32 456

q3 100 54 114 14 264

mean 63 50 95 10 172

Figure 2-19. Insulation material box plot, duration, AC tests

2.9 Insulation-Jacket Type Combinations

The previous two sections evaluated the effects of conductor insulation type and materials. The

next logical parameter to evaluate would be cable jacket materials and polymer types. Although

this was done initially, a review by the electrical expert PIRT panel found that the analysis was

less than useful, and it was suggested that the synergistic effects of cable jacket type and cable

insulation type should be evaluated instead.

This section provides that evaluation by looking at the insulation/jacket polymer type

combinations available from the test data. This evaluation creates three bins, which include

cables with (1) TP insulation and TP jacket, (2) TS insulation and TS jacket, and (3) TS

insulation and TP jacket (mixed cable type). Table 2-19 and Figure 2-20 present the failure

mode likelihood information, while Table 2-20 and Figure 2-21 reference the duration data for

these configurations. The likelihood information provides little value in identifying any influence

by insulation/jacket types on a particular failure mode. The duration evaluation indicates that

the TS-TS cables have longer durations in general than the TP-TP and TS-TP configurations,

based on the mean and the inter-quartile range.

0

100

200

300

400

EPR XLPE PE PVC TEF EPR XLPE PE PVC TEF

TS TP TS TP

Hot Short SpuriousOperation

Secnods

q1

min

median

max

q3

1345 453s

s

456s 456s

2-20

Table 2-19. Insulation-jacket type, global approach, AC tests

Global Approach TP-TP TS-TS TS-TP

Fuse Clear 17 20 8

Hot Short 22 36 9

Spurious Operation 20 29 9

HS/SO Possible 39 56 17

Figure 2-20. Insulation-jacket type column plot, global approach, AC tests

Table 2-20. Insulation-jacket type, duration data, AC tests

Hot Short Spurious Operation

TP-TP TS-TS TS-TP TP-TP TS-TS TS-TP

q1 5 12 7.6 6 16.7 14.45

min 0.2 0.4 0.2 0.2 0.6 0.8

median 23.3 43.2 24 24 47.6 27.1

max 456 1345 62.4 456 231 62.4

q3 96.6 94.6 32.9 64.2 96.3 43.05

mean 79.8 76.1 23.1 73.4 61.9 28.8

TP-TP TS-TS TS-TP

Count

0

10

20

30

40

50

60

Fuse Clear

Spurious Operation

HS/SO Possible

100%

44%

56%

51%

36%

64%

52%

100%

47%

53%

2-21

Figure 2-21. Insulation-jacket type box plot, duration, AC tests

2.10 CPT Size

Several differently sized control power transformers (CPTs) were used in the testing to evaluate

the effects of CPT size on fire-induced circuit response. Table 2-21 provides information on the

size of CPTs used during the various testing projects. At the time of this writing, the authors

were not able to determine the size of the CPTs used in the NEI/EPRI testing project; thus, this

data has been separated into its own bin for this review.

Table 2-21. Test project CPT size

75VA 100VA 150VA 200VA Unknown Size No CPT

NEI/EPRI X X

CAROLFIRE X X X X

DESIREE-FIRE X X X X

Table 2-22 and Figure 2-22 provide the circuit fault modes based on variously sized CPTs used

during testing. The limited number of tests (two in total) using the 75VA CPT, and the fact that

one test cleared the fuse while the other resulted in a spurious operation; provide little

information on this configuration’s effect on failure mode. The 100VA and 150VA data are very

similar to the ~32-33% ground fault mode likelihood and the ~65-67% hot short/spurious

operation likelihood. The 200VA CPT and no CPT data are also similar to the ground fault

likelihood of ~40-41% and the spurious operation likelihood of ~50-53%.

The NEI/EPRI data doesn’t conform to the fault mode characteristics of the SNL data, as it

shows a much higher likelihood of ground faults (~59%), a lower likelihood of hot shorts (~41%),

and a much lower likelihood of spurious operations (~18%). Although there are many aspects

within the NEI/EPRI testing that could lead to these results, the authors are unable to pinpoint

the exact cause of the differences between the NEI/EPRI test data and the other data.

0

100

200

TP‐TP TS‐TS TS‐TP TP‐TP TS‐TS TS‐TP

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

456s 1345s 456s 231s

2-22

Table 2-22. CPT size, global approach, AC tests

Global Approach 75VA 100VA 150VA 200VA Unknown

Size (EPRI) None

Fuse Clear 1 5 10 7 10 12

Hot Short 1 10 21 10 7 18

Spurious Operation 1 10 20 9 3 15

HS/SO Possible 2 15 31 17 17 30

Figure 2-22. CPT size column plot, global approach, AC tests

Table 2-23 and Figure 2-23 present the duration data segregated by CPT size. The data shows

that the hot short and spurious operation duration for cases where no CPT is used is on

average longer than when a CPT is used. In general, there is not much difference between the

CPT size and the duration of the hot short or the spurious operation.

Table 2-23. CPT size, duration data, AC tests

75VA 100VA 150VA 200VA EPRI None

q1 21 4 5 7 12 18

min 9 1 1 1 6 1

median 32 38 24 10 21 57

max 52 453 320 238 198 1345

q3 42 65 54 41 57 120

mean 31 67 53 47 50 108

Spurious Operation

75VA 100VA 150VA 200VA EPRI None

q1 37 5 9 7 24 22

min 32 1 1 1 18 6

median 42 38 30 10 54 60

max 52 97 296 231 198 456

q3 47 62 61 42 120 114

mean 42 37 56 46 83 83

75VA 100VA 150VA 200VA Unknown Size None

Count

0

10

20

30

40

Fuse Clear

Spurious Operation

HS/SO Possible

100%

65%

100%

50%

33%

67%

32%

68%

41%

59%

53%

59%

41%

18%

40%

60%

50%

2-23

Figure 2-23. CPT size box plot, duration, AC tests

2.11 Circuit Grounding

This section explores how circuit grounding affects fire-induced AC circuit response by

examining the effects of having a grounded versus an ungrounded AC power supply on the fault

mode likelihood during fire exposures. For grounded AC circuits that are powered from a CPT,

the neutral on the secondary side of the CPT would be connected to the ground. For a

grounded AC circuit not using a CPT, but connected directly to outlet power, the neutral would

be grounded. The circuit ground connection for the experiments is the same ground plane

associated with the cable raceway, cable trays, and conduits. Ungrounded AC circuits tested in

the NRC tests are identical to the grounded circuits with the one exception of the common

return of the power supply not being connected to ground. No data from circuits powered by a

DC power supply has been included in this section.

Table 2-24 and Figure 2-24 provide the ground fault, spurious operation, and hot short fault

mode information. The data indicates that circuits that are ungrounded have a higher likelihood

of experiencing a hot short (~85%) than a circuit that is grounded (~58%). Looking at the data

in the fuse clearing aspects, a grounded circuit has a higher chance of clearing a fuse (~42%)

than an ungrounded circuit (~15%). For the grounded configurations, 3% of the fuse clears are

attributed to seven test points that used armored cable. DC testing by NEI/EPRI, Duke Energy

Corporation, and the U.S. Nuclear Regulatory Commission (NRC) has shown that when an

armored cable is used in a grounded circuit, the likelihood of experiencing a fuse clear failure is

approximately 1.

Table 2-24. Circuit grounding, global approach, AC tests

Global Approach Un-Grounded Grounded

Fuse Clear 2 41

Hot Short 11 56

Spurious Operation 11 47

HS/SO Possible 13 97

0

100

200

300

75VA

100VA

150VA

200VA

EPRI

None

75VA

100VA

150VA

200VA

EPRI

None

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

453s 320s 1345s 456s

2-24

Figure 2-24. Circuit grounding column plot, global approach, AC tests

Table 2-25 and Figure 2-25 present the duration data segregated by circuit grounding

(grounded versus ungrounded). The data indicates that the grounded circuits have a slightly

higher average duration time, but the ranges of durations shown in Figure 2-25 indicates few

differences.

Table 2-25. Circuit grounding, duration data, AC tests

Hot Short Spurious Operation

Grounded Ungrounded Grounded Ungrounded

q1 8 7 10 16

min 1 1 1 1

median 24 29 31 33

max 1345 224 456 121

q3 84 62 84 71

Mean 74 44 63 45

Figure 2-25. Circuit grounding box plot, duration, AC tests

Not Gnd Gnd

Count

0

20

40

60

80

100

120

Fuse Clear

Spurious Operation

HS/SO Possible

100%

15%

85%

42%

58%

48%

100%

0

40

80

120

160

Gnd UnGnd Gnd UnGnd

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

1345s 224s 456s

2-25

2.12 Wiring Configuration

Wiring configuration refers to the number of sources, targets, and neutrals/grounds located

within a cable of interest. This parameter evaluation does not evaluate circuit-to-conductor

connection patterns within a cable. EPRI conducted an evaluation of conductor connection

patterns and determined that the “source-centered” configuration resulted in the highest

likelihood of a circuit experiencing a hot short. The NRC-sponsored CAROLFIRE and

DESIREE-FIRE projects typically connected circuits in the source-centered configuration. Thus,

there is little to no new data to provide an evaluation of conductor connection patterns.

Table 2-26 provides a breakdown of the three wiring configurations and the number of source,

target, and common return conductors in each configuration. A vast majority of the tests used a

common configuration with two (2) energized source conductors, four (4) target conductors

(passive targets, active targets, and spares), and one (1) common power supply return

conductor (either a ground or a neutral, depending on circuit grounding configuration).

Table 2-27 and Figure 2-26 present the spurious operation likelihood information by wiring

configuration.

Table 2-26. Wiring configurations

Sources # Targets # Returns

Configuration 1 2 4 1

Configuration 2 2 3 1

Configuration 3 2 2 1

Table 2-27. Wiring configuration, global approach, AC tests

Global Approach Config. 1 Config. 2 Config. 3

Fuse Clear 41 1 3

Hot Short 65 1 1

Spurious Operation 56 1 1

HS/SO Possible 106 2 4

Figure 2-26. Wiring configuration column plot, global approach, AC tests

Config. 1 Config. 2 Config. 3

Count

0

20

40

60

80

100

120

Fuse Clear

Spurious Operation

HS/SO Possible

100%

39%

61%

53%

50%

100%

75%

25%

100%

2-26

The duration data is difficult to interpret for this parameter due to the lack of data for

configurations 2 and 3. Table 2-28 and Figure 2-27 present the duration data based on wiring

configuration.

Table 2-28. Wiring configuration, duration data, AC tests

Hot Short Spurious Operation

Config. 1 Config. 2 Config. 3 Config. 1 Config. 2 Config. 3

q1 7 8 1 10 15 1

min 1 6 1 1 15 1

median 27 10 1 33 15 1

max 1345 15 1 456 15 1

q3 79 12 1 81 15 1

mean 69 10 1 61 15 1

Figure 2-27. Wiring configuration box plot, duration, AC tests

2.13 Conductor Size

Control cables used in nuclear power plants (NPPs) are typically constructed with # 12 or # 14

American wire gauge (AWG) conductors. From the test data, only one AC MOV test used a

cable conductor size outside of this range, and it was a 3/C # 8 AWG cable using a modified

MOV circuit. To evaluate this parameter, the conductor size data was segregated into three

bins, <12 AWG, 12 AWG, and 14 AWG. All of the 14 AWG data came from the NEI/EPRI

testing project. The 12 AWG bin contains test data from all three test projects, and the single

<12 AWG data point came from the CAROLFIRE project.

Table 2-29 and Figure 2-28 present the test data segregated by conductor size in tabular and

graphical format. From this data, there is no direct indication that conductor size has any effect

on the hot short likelihood. However, a comparison of the spurious operation likelihood between

12 AWG and 14 AWG (NEI/EPRI tests) indicates that there is a lower likelihood for 14 AWG

conductor cables to experience a spurious operation. Although this is what the data shows, the

0

20

40

60

80

100

Config. 1 Config. 2 Config. 3 Config. 1 Config. 2 Config. 3

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

1345s 456s

2-27

authors believe that some other parameter is influencing this outcome, possibly the EPRI CPT

circuit data, which showed low spurious operation probability.

Table 2-29. Conductor size, global approach, AC tests

Global Approach <12 AWG 12 AWG 14 AWG

Fuse Clear 1 30 14

Hot Short 0 47 20

Spurious Operation 0 43 15

HS/SO Possible 1 77 34

Figure 2-28. Conductor size column plot, global approach, AC tests

Table 2-30 and Figure 2-29 present the duration data based on the conductor size bins. The

data indicates that the smaller 14 AWG conductor cables have a longer duration (60 second

median) than 12 AWG conductor-sized cables (24-27 second median).

Table 2-30. Conductor size, duration data, AC tests

Hot Short Spurious Operation

<12 AWG 12 AWG 14 AWG <12 AWG 12 AWG 14 AWG

q1 - 7 15 - 8 18

min - 1 1 - 1 6

median - 24 60 - 27 60

max - 453 1345 - 296 456

q3 - 55 120 - 56 120

mean - 52 115 - 49 94

<12 AWG 12 AWG 14 AWG

Count

0

20

40

60

80

100

Fuse Clear

Spurious Operation

HS/SO Possible

100%

0%

100%

39%

61%

56%

100%

41%

59%

44%

2-28

Figure 2-29. Conductor size box plot, duration, AC tests

2.14 Water Based Fire Suppression Effects on AC Circuit Failures

The effect of water spray on thermally fragile cables was only explored in a minimal set of tests.

During the NEI/EPRI tests, a single sprinkler head was located in the ceiling corner of the fire

test enclosure above the cable tray bend in the general fire location. The sprinkler was

manually activated, and it was not used in every test. There were also a few tests in which

manual water suppression was applied using a garden hose. In CAROLFIRE, a single open

head sprinkler was installed near the ceiling center of the intermediate-scale test structure, on a

pendant about 150 mm (6 in.) long. The water flow was manually initiated using a small electric

pump and only initiated in those tests where one or more of the cables had not experienced

electrical failure (silicone rubber). No water suppression was used in the DESIREE-FIRE

testing.

Water spray was observed to cause spurious operations in only one NEI/EPRI test, Test 3. In

this case, a spurious operation did coincide with water spray, and persisted for approximately 24

seconds before a fuse clear occurred. This test cable was located at the center of the top layer

of a two-layer cable fill test. Figure 2-30 provides a voltage plot of test circuit 3 for NEI/EPRI

Test #3, showing the spurious operation on the target conductor, Wire #4 but only hot shorts on

non-spurious operation target Wire #5 and Wire #7.

0

40

80

120

160

200

<12 AWG 12 AWG 14 AWG <12 AWG 12 AWG 14 AWG

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

453s 1345s 296s 456s

2-29

Figure 2-30. NEI/EPRI test 3 voltage plot - water spray

In Test 10 of the EPRI program, water spray was applied during an ongoing spurious operation.

The application of water terminated the spurious operation (cleared for 42 seconds), followed by

a brief operation of a target conductor (6 seconds), followed by a fuse clear failure. These

electrical interactions are shown in Figure 2-31. In two other tests, water spray showed

marginal effects on the cable electrical response. In one case, an induced voltage had built

upon the spare conductor. When water spray was initiated, the induced voltage was rapidly

lost. In the other case, very minimal current spikes (~0.05 amps) were observed in the 1/C

cables, coincident with water application. The reader is encouraged to refer to the EPRI test

report for more information.

Time (s)

4500 4520 4540 4560 4580 4600 4620 4640 4660

Voltage (V)

-20

0

20

40

60

80

100

120

140

7/C Wire #1

7/C Wire #2

7/C Wire #4

7/C Wire #5

7/C Wire #7

Application of Water

2-30

Figure 2-31. NEI/EPRI test 10 voltage response following water spray

The CAROLFIRE intermediate-scale tests used the water sprinkler in five tests (IT5, IT6, IT9,

IT10, IT13). In all of these tests, the only cable types operating at the time of manual sprinkler

activation were the Silicone Rubber or Vita-Link cables. In one instance, the sprinkler activation

caused an SR cable to fail in a manner that resulted in a spurious operation. All other cables

exposed to the water spray were connected to the insulation resistance measurement system.

Of those seven cables, six resulted in a short circuit of less than 1,000 ohms5

. A single cable

experienced a short circuit of less than 1,000 ohms, followed momentarily by some insulation

resistance recovery above 1,000 ohms.

Another complicating matter for evaluating water spray effects on cable response is that water

suppression was applied near the end of the testing, and many of the circuits had already

experienced fuse clear circuit failures. Although there is data available on the effects of water

spray on thermally fragile cables, an understanding of the cables’ response to water at earlier

stages of cable damage is unavailable at this time.

5

1,000 ohms was used as the insulation resistance threshold for failure of a cable. Insulation resistance measurements under

1,000 ohms indicate that insulation is not capable of performing its design function.

Time (s)

4400 4600 4800 5000 5200 5400 5600 5800

Voltage (V)

0

20

40

60

80

100

120

140

1/C Wire #1

1/C Wire #2

1/C Wire #3

Water Applied

2-31

2.15 AC Circuit Concurrence of Hot Short-Induced Spurious

Operations

Concurrence of hot short-induced spurious operations, as discussed in this report, occurs when

more than one circuit (or cable) experiences individual spurious operations at the same time

(i.e., concurrence). The AC test circuit configurations eliminated the possibility of a single cable

causing multiple concurrent hot short-induced spurious operations. Thus, when reviewing the

test results, two cables must experience a hot short-induced spurious operation at the same

time to be considered concurrent.

In all of the AC testing to date, the concurrence of spurious operations or hot shorts has not

been observed within any individual test. In some cases, the concurrence between two circuits

was missed by only a few seconds, but, given the strict definition of concurrent hot shortinduced spurious operations, this phenomenon was not observed in any AC circuit testing.

There are several reasons that this phenomenon was not observed in testing. First, only a

limited number of cables/circuits can be instrumented electrically during each test. The

NRC/SNL small-scale radiant testing was limited to two electrically instrumented cables per test,

while the larger scale testing (both industry- and NRC-sponsored) was limited to four surrogate

AC MOV circuits for the AC testing. Secondly, the exposure conditions for the majority of the

test were fairly intense, as the tests were designed to cause failure within 10-30 minutes for a

risk-significant scenario. These intense exposures resulted in the cables quickly cascading

through failure modes, as well as shorter spurious operation durations. Thirdly, a variety of

cable types were tested (especially in the NRC/SNL testing), and each cable type has a unique

thermal failure threshold; thus, even with fairly uniform exposure conditions for multiple cables,

the failure times may never align in the testing because of differing cable thermal failure

thresholds. Lastly, the larger scale testing allowed for a variety of thermal exposure conditions

due to the locations of the cables relative to the heat source and their locations within a tray

loaded with cables. For instance, a cable located on the bottom row of cables in an open

ladder-back cable tray in a fire plume will be exposed to more intense thermal conditions than a

cable in the same cable tray, but insulated from the fire conditions by other cables.

During a PIRT panel meeting, it was suggested that the NRC/SNL tests could be combined

based on exposure location in the intermediate-scale test apparatus to evaluate their likelihood

of concurrence. As the thermal exposures were kept fairly constant among the NRC/SNL

intermediate-scale tests (~200kW), this concept was explored.

To complete this comparison, the intermediate-scale test data from CAROLFIRE and the

intermediate-scale AC test data from DESIREE-FIRE were combined and separated by

location. As shown in Figure 2-32, the locations were labeled differently between projects, so

care was taken to ensure that labeling differences did not lead to binning errors. Symmetrical

cable locations were grouped together as one location because of identical exposure conditions.

For example, in the CAROLFIRE configuration in Figure 2-32(a), locations E and G were

grouped together, as well as locations C and E of the DESIREE-FIRE configuration in Figure 2-

32(b). However, locations C and F of CAROLFIRE and locations B and D of DESIREE-FIRE

were not grouped together because the plume transition zone near the top location (F in

CAROLFIRE, D in DESIREE-FIRE) likely has different exposure conditions than the location

directly below. Trays grouped by location would be exposed to the same fire conditions, heat

release rate, and location relative to the wall. The data from all AC NRC tests was then

analyzed to find times when multiple hot short-induced spurious operations occurred in the

2-32

same physical location at the same time (i.e., concurrence). The data was also processed to

account for the electrical and mechanical interlocks that would typically be used in NPP

applications, but were not used during testing. For instance, the MOV starters have two active

targets that, if energized by a fire-induced hot short, would be classified as hot-short induced

spurious operations by the testing protocol. In reality, however, only one MOV contactor can be

energized at a time. Thus, the data was post-processed to represent circuit response in NPP

applications where the interlocks would be used.

(a) (b)

Figure 2-32. (a) CAROLFIRE and (b) DESIREE-FIRE intermediate-scale exposure location

designation

Analyzing the data in this manner confirms that concurrent hot short-induced spurious

operations were observed in CAROLFIRE/DESIREE-FIRE location A and CAROLFIRE location

G/E (DESIREE-FIRE location C/E), “upper hot gas layer,” when the individual test data was

grouped together. Conductors C5 and C6 are the active targets in the AC MOV circuits, which

represent spurious operations/hot short targets. The draft version of this report contained

concurrence of conductors C4 and C8, which are the passive targets and represent only hot

short targets. A public comment noted that the inclusion of the hot short data made the results

difficult to interpret and provided little value in evaluating multiple spurious operations. As such,

the data for conductors C4 and C8 has been removed from the plots.

At location A, two sets of concurrence were identified, as shown in Figure 2-33 and Figure 2-34.

The blue diamonds in these figures indicate the start of a hot short-induced spurious operation,

the red squares indicate the end, and the line between them represents the duration. A

concurrence occurs when hot shorts within different cables have overlapping times. The

information on the horizontal axis indicates:

 test series (C = CAROLFIRE),

 testing scale (IT = Intermediate, P = Penlight),

 test number,

 circuit number (CK#), and

 the conductor that experienced the hot short (C#).

2-33

Figure 2-33. Concurrent hot shorts - Location A - 4 cables

Figure 2-33 shows the first set of concurrences to be identified, which included four cables,

none of which were the same cable type (XLPO/XLPO6

, EPR/CPE, TEF/TEF, and XLPE/PVC).

The data set representing location A consisted of 25 test cables, which resulted in 17 spurious

operations. Of the 17 operations involving the four cables, there were 10 instances where two

cables experienced hot short-induced spurious operations concurrently. Five of these 10

instances involved three cables. Concurrences that only involve spurious operation targets are

identified in Table 2-31, along with the durations of these concurrences. In this table, the test

circuits are identified on the vertical and horizontal axes, and any concurrences are identified by

a number that represents the duration (in seconds) of the concurrence. This table also presents

the start and stop times for the individual circuit spurious operations at the bottom of the table.

In Table 2-31, for example, a value of 2.6 in the top row indicates that test “C-IT-6-CK4-C5” and

test “C-IT-7-CK2-C5” experienced a concurrent spurious operation for 2.6 seconds. This value

can be confirmed by looking at the individual circuit spurious operation start and stop times: “CIT-6-CK4-C5” experienced a spurious operation starting at 268.8 seconds and ending at 272.8

seconds, while “C-IT-7-CK2-C5” experienced a spurious operation starting at 250.4 seconds

and ending at 271.4 seconds. Thus, from 268.8 to 271.4 seconds, both circuits experienced

spurious operations. It should also be pointed out that the table is presented such that the

values to the right of the diagonal shaded boxes mirror the values to the left of the diagonal

shaded boxes. The last column in the table presents the number of cables involved in

concurrent operations. For instance, the top row indicates that three cables were involved in

concurrent spurious operations (SOs). These three cables were identified as “C-IT-6-CK4-C5,”

“C-IT-7-CK2-C5,” and “C-IT-11-CK4-C6.”

6

A typical convention for identifying a cable’s insulation and jacket materials is to write the insulation material first, followed by the

jacket material. For example, XLPE/PVC is a cross-link polyethylene (XLPE) insulated cable with a polyvinyl chloride (PVC) jacket.

220.0

230.0

240.0

250.0

260.0

270.0

280.0

Time (s)

start

stop

2-34

Table 2-31. Concurrent spurious operation durations – test Location A

(concurrence time shown in seconds)

Test ID

C-IT-6-CK4-C5

c-IT-6-CK4-C6

C-IT-7-CK2-C5

C-IT-7-CK2-C6

C-IT-10-CK3-C5

C-IT-11-CK4-C5

C-IT-11-CK4-C6

C-IT-11-CK4-C5

C-IT-11-CK4-C6

of concurrent

cable SOs

C-IT-6-CK4-C5 - 2.6 - - - - - 4 3

C-IT-6-CK4-C6 - 4.8 - - - - - 4.8 3

C-IT-7-CK2-C5 2.6 4.8 - - 2.8 1 2.8 10.8 3

C-IT-7-CK2-C6 - - - 7.8 7.8 - - - 3

C-IT-10-CK3-C5 - - - 7.8 - - - - 2

C-IT-11-CK4-C5 - - 2.8 7.8 - - - - 2

C-IT-11-CK4-C6 - - 1 - - - - - 2

C-IT-11-CK4-C5 - - 2.8 - - - - - 2

C-IT-11-CK4-C6 4 4.8 10.8 - - - - - 3

Start Time 268.8 264.0 250.4 227.2 225.0 242.6 253.2 254.2 260.6

Stop Time 272.8 268.8 271.4 250.4 235.0 253.2 254.2 257.0 276.0

Duration 4.0 4.8 21.0 23.2 10.0 10.6 1.0 2.8 15.4

Figure 2-34 presents the second set of concurrences that occurred in location A. Here, again,

different cable types were involved (XLPE/PVC and PE/PVC). There is only one instance in

which multiple spurious operations occurred concurrently. Here circuit three of Test 7

experiences a spurious operation at the same time as circuit two of Test 8.

Figure 2-34. Concurrent hot shorts - Location A - 2 cables

375

380

385

390

395

400

405

410

415

C‐IT‐7‐CK3 c5 C‐IT‐8‐CK2 c5

Time (s)

start

stop

2-35

The other instance in which concurrent hot shorting was identified in this analysis was in the

upper hot gas layer exposure locations (CAROLFIRE location G/E, DESIREE-FIRE location

C/E). In these locations the data represents 20 test cables. Of these 20 cases, 12 spurious

operations occurred, with 14 instances of concurrence. The only set of concurrences included

four cables, of which three were of the same construction (PE/PVC) and the other was

PVC/PVC. All were of the thermoplastic polymer variety. Figure 2-35 presents a plot of the hot

short-induced spurious operation durations, and Table 2-32 provides a listing of the circuits

involved in spurious operation concurrences and associated durations. The durations of these

concurrences are longer than those in Location A, likely due to the difference in thermal

exposure conditions.

Figure 2-35. Concurrent hot shorts - upper hot gas layer - 4 cables

625

675

725

775

825

875

925

975

1025

1075

1125

C‐IT‐11‐CK2 c5

C‐IT‐12‐CK2 c6

C‐IT‐9‐CK4 c5

C‐IT‐9‐CK4 c6

C‐IT‐10‐CK1 c5

C‐IT‐10‐CK1 c6

Time (s)

stop

start

(0.8s)

2-36

Table 2-32. Concurrent spurious operations – upper hot gas layer Test ID C-IT-11-CK2-C5 C-IT-9-CK4-C5 C-IT-12-CK2-C6 C-IT9-CK4-C6 C-IT10-CK1-C6 C-IT-10-CK1-C6 C-IT-10-CK1-C5 C-IT-10-CK1-C6 # of concurrent cable SO’s

Test ID

C-IT-11-CK2-C5 38.2 97.4 47.4 0.8 31 10.8 - 4

C-IT-9-CK4-C5 38.2 25.8 - - - - - 3

C-IT-12-CK2-C6 97.4 25.8 47.4 0.8 53 81.4 46.4 4

C-IT-9-CK4-C6 47.4 - 47.4 20.4 6.8 - - 4

C-IT-10-CK1-C6 0.8 - 0.8 20.4 - - - 4

C-IT-10-CK1-C5 31 - 53 6.8 - - - 4

C-IT-10-CK1-C6 10.8 - 81.4 - - - - 3

C-IT-10-CK1-C6 - - 46.4 - - - - 2

Start Time (s) 658.0 776.2 788.6 814.4 841.4 855.0 875.2 910.2

Stop Time (s) 886.0 814.4 1084.8 861.8 842.2 908.0 956.6 956.6

Duration (s) 228.0 38.2 296.2 47.4 0.8 62.0 81.4 46.4

The rest of the locations showed no instances of concurrence. Four tests were run using

CAROLFIRE location B/D, ten tests were run using CAROLFIRE location C (DESIREE-FIRE

location B), and fourteen tests were run using CAROLFIRE location F (DESIREE-FIRE location

D). None of these tests produced any instances of hot short concurrences. Section 4.15

provides the concurrent hot shorting for the dc circuits tested in the DESIREE-FIRE project.

3-1

3. INTER-CABLE – ALTERNATING CURRENT CIRCUITS

The evaluation of circuit failure results becomes increasingly complex when more than one

cable is involved in the electrical failure. Cable-to-cable interactions are referred to as “intercable,” and, for an inter-cable hot short to occur, a source conductor in one cable must come

into electrical contact with a target conductor in a different cable.

The number of recorded cable-to-cable interactions from the AC tests is significantly lower than

the number of intra-cable interactions (within a cable). Thus, testing to date has provided only a

small pool of data from which to draw conclusions about the effects of parameters on the

likelihood and duration of these inter-cable interactions. Even with these limitations, there are

some conclusions that can be drawn from the data. These conclusions are presented below

and may provide some insight into the influencing factors of inter-cable electrical interactions.

This section will not systematically evaluate parameter effects on the fire-induced circuit failure

response, as was done in the previous section for the intra-cable evaluation.

All of the major testing projects (Electric Power Research Institute/Nuclear Energy Institute

(NEI/EPRI), Cable Response to Live Fire (CAROLFIRE), and Direct Current Electrical Shorting

In Response to Exposure Fire (DESIREE-FIRE)) provide at least two test configurations to

evaluate the occurrence of inter-cable failures. In most cases, the voltage and current

measurements from the simulated circuit could be evaluated to determine whether any intercable interactions occurred. In addition, separate circuit configurations were used in all test

programs to specifically focus on understanding, and, in some cases, stacking the odds to

trigger inter-cable interaction. The following provides a description of how the tests were

conducted and what results were achieved.

Figure 3-1 provides an illustration of how the cables were oriented within a cable tray for the

inter-cable tests during the NEI/EPRI program. Cables 1-3 were monitored for electrical

response, with cables 1 and 3 containing both energized source conductors and target

conductors, while cable 2 only contained target conductors. The target conductors were

connected to burden resistors to simulate a load. The black cables in Figure 3-1 represent fill

cables that were not monitored for electrical response, but were used as a buffer between the

electrically monitored cables and the metallic cable tray. These fill cables likely reduced the

likelihood of an energized source coming in contact with the ground plane and causing a fuse

clear failure.

Figure 3-1. NEI/EPRI inter-cable test tray fill

Two NEI/EPRI tests used this configuration, and both tests showed similar results. The voltage

and current readings indicate that the cables failed internally prior to any external interactions

between cables. Since this configuration didn’t represent system circuits used in plants, it is

3-2

difficult to determine whether or not inter-cable interactions would have caused hot shorts of

sufficient quality to result in a component repositioning in an actual plant system.

The CAROLFIRE inter-cable test set-up was slightly different in that all of the conductors in two

multi-conductor cables were energized as sources and a third multi-conductor cable had all of

its conductors connected to a motor starter contactor, a target. Thus, the CAROLFIRE circuit

could detect inter-cable interactions, but was unable to recognize when conductors internal to

the multi-conductor cables had failed. The CAROLFIRE inter-cable test set-up is shown in

Figure 3-2.

Figure 3-2. CAROLFIRE inter-cable test tray fill

Twelve inter-cable circuit trials were used in a total of four intermediate-scale fire tests during

CAROLFIRE. Three of these circuits were left ungrounded, resulting in no possibility for the

circuit fuse to clear. Because of this configuration, hot shorts/spurious operations were

inevitable, and, in all three instances, prolonged spurious operations did occur. Of the

remaining nine test circuits, seven experienced fuse clear faults. The remaining two circuits,

both from test IT-3, experienced some inter-cable induced voltages, although this was not

sufficient to cause a spurious operation. The CAROLFIRE inter-cable failure data does not

provide a strong basis for understanding the inter-cable shorting phenomenon. In actual fires

involving energized control cables for safety significant systems, there is a competing factor

between the conductors internal to the failing cable and any inter-cable interactions. It is

unfortunate that the CAROLFIRE results could not provide more insights into this competitive

factor.

As discussed above, all three testing programs used surrogate motor-operated valve (MOV)

circuits to monitor cable electrical response during a fire test. A review of this data can provide

information on how the cable fails internally versus failing externally. However, before looking at

this data, it is important to understand some of the differences between the NEI/EPRI and U.S.

Nuclear Regulatory Commission/Sandia National Laboratories (NRC/SNL) test arrangements.

First, the industry tests used a configuration in which a 7/C cable was surrounded by three

individual 1/C insulated conductors (without jacketing), zip-tied to the 7/C cable. This

configuration is shown in Figure 3-3. The 7/C cable contained source, target, spare, and neutral

conductors, while the exterior single conductors were either an energized source or an active

target. All energized conductors were powered by the same source (wall power or control

power transformer (CPT)). It should be noted that this configuration is not commonly found in

U.S. nuclear power plants (NPPs). If single conductor cables are used, they will typically have a

protective jacket over the single conductor insulation. The NEI/EPRI testing simply used an

unjacketed insulated conductor that was stripped from a multi-conductor cable. That said, the

results are still valuable and may be considered more conservative in that this configuration may

3-3

increase the likelihood of inter-cable interactions because of the lack of jacket and the use of

cable ties to keep the single conductors in close proximity to the 7/C cable.

Figure 3-3. NEI/EPRI cable configuration

The NEI/EPRI test results indicate that of the 17 test circuit device spurious operations that

experienced inter-cable spurious operation(s), seven were between the 1/C cables. In four

cases, the 7/C cable acted as a source to a 1/C cable target, and, in six cases, a 1/C cable

energized a target conductor in a 7/C cable. Table 3-1 presents the results of the NEI/EPRI

inter-cable results.

Table 3-1. NEI/EPRI inter-cable failure characteristics

Test ID Source Cable

(#/C, wire, insulation)

Target Cable

(#/C, wire, insulation) Duration (seconds)

Test 3, Circuit 1, Device 3 1/C – S1 (TS) 1/C – S3 (TS) 6

Test 4, Circuit 2, Device 3 1/C – S2 (TP) 1/C – S3 (TP) 66

Test 4, Circuit 3, Device 3 1/C – S2 (TP) 1/C – S3 (TP) 342

Test 4, Circuit 4, Device 1 1/C – S1&S2 (TP) 7/C – W5 (TP) 54

Test 4, Circuit 4, Device 2 1/C – S1&S2 (TP) 7/C – W4 (TP) 12

Test 4, Circuit 4, Device 3 7/C – W2 (TP) &

1/C – S2 (TP) 1/C – S3 (TP) 318

Test 6, Circuit 1, Device 1 1/C – S2 (TP) 7/C – W5 (TP) 192

Test 6, Circuit 1, Device 2 1/C – S2 (TP) 7/C – W4 (TP) 282

Test 6, Circuit 1, Device 3 1/C – S2 (TP) 1/C – S3 (TP) 492

Test 6, Circuit 2, Device 3 7/C – W2 (TP) 1/C – S3 (TP) 606

Test 8, Circuit 1, Device 3 1/C – S2 (TS) 1/C – S3 (TS) 18

Test 9, Circuit 4, Device 3 1/C – S2 (TS) 1/C – S3 (TS) 6

Test 10, Circuit 2, Device 3 1/C – S1 (TS) &

7/C – W2 (TS) 1/C – S3 (TS) 804

Test 10, Circuit 4, Device 3 1/C – S2 (TS) 1/C – S3 (TS) 486

Test 12, Circuit 3, Device 3 7/C – W1 (TS) 1/C – S3 (TS) 12

Test 17, Circuit 1, Device 1 1/C – S2 (TP) 7/C W5 (TP) 66

Test 17, Circuit 1, Device 2 1/C – S2 (TP) 7/C W4 (TP) 66

In the CAROLFIRE testing, multi-conductor cables were connected to individual surrogate

circuit diagnostic units (SCDUs) and arranged in 3- or 6-cable triangular bundles. The results

from the CAROLFIRE SCDU testing where inter-cable interactions were observed are shown in

3-4

Table 3-2. CAROLFIRE did not use NEI configuration. All inter-cable interactions were from

adjacent cables.

Table 3-2. CAROLFIRE AC inter-cable failure characteristics

Test ID

Source Cable

(Circuit, Insulation)

Target Cable

(Circuit, Insulation)

Duration

(seconds)

Test IP 4, Circuit 1* Circuit 2, TP 7/C – W6, TP 1

Test IP 4, Circuit 3* Circuit 2, TP 7/C – W5 & W6, TP 1

Test IP 4, Circuit 4 Circuit 2, TP 7/C – W6, TP 1

Test 1, Circuit 4* Circuit 1, TS 7/C – W4 (HS), TS 1

Test 7, Circuit 2* Circuit 3, TS 7/C – W4 (HS), TS 1

Test 8, Circuit 2* Circuit 3, TS 7/C – W4 (HS), TP 44

Indicates inter-cable interactions occurring after the circuit fuse cleared.

In the CAROLFIRE project, the insulation resistance measurement system (IRMS) was used

during Penlight radiant exposure tests and during the intermediate-scale testing. The IRMS can

detect the onset of inter-cable shorting behavior, can measure the relative timing of inter-cable

shorting versus both intra-cable shorting and shorts to the external ground, and can measure

the duration of inter-cable shorts (i.e., how long an inter-cable conductor-to-conductor short

remains independent of the external ground) [NUREG/CR-6931, V1].

The CAROLFIRE tests did detect some cases of inter-cable shorting between thermoset (TS)

cables; however, only one of these cases involved a clear-cut case of a sustained inter-cable

short circuit between two TS cables (IRMS in Test IT-1) that could have led to a spurious

operation. In other cases, the interactions were secondary or tertiary failure modes for at least

one of the two involved cables. However, the test data clearly showed that TS-to-TS

interactions are plausible, although the likelihood of risk-relevant interactions appears to be low,

especially in comparison to the likelihood of intra-cable interactions leading to spurious

operation [NUREG/CR-6931].

4-1

4. INTRA-CABLE – DIRECT CURRENT CIRCUITS

All of the fire-induced DC circuit failure data and information available for the analysis

documented in this report came from the U.S. Nuclear Regulatory Commission (NRC)–

sponsored Direct Current Electrical Shorting In Response to Exposure Fire (DESIREE-FIRE)

project. A substantial amount of effort was required to convert the dc data into a usable format

for this work. The formatting was handled by Sandia National Laboratories (SNL), and led to

identification of several errors documented in the draft test report for the DESIREE-FIRE

project. These errors were subsequently corrected in the final version of NUREG/CR-7100,

“Direct Current Electrical Shorting In Response to Exposure Fire (DESIREE-FIRE): Test

Results.”

The only dc test data removed from the analysis were instances where the cable did not reach a

failure point at the end of the test. The majority of these cases were for the Kerite cable testing,

where it was important to stop the test prior to cable failure to evaluate the physical damage to

the cable materials. Tests excluded from further analysis in this report included the following:

 D-P-27-MOV1

 D-P-27-MOV2

 D-P-26-SOV1

 D-P-26-SOV2

 D-P-38-SOV1

 D-P-38-SOV2

 D-IT-P1-1-Vlv

 D-IT-P1-LargeCoil

Section 4.1 details the specific set points used to clean up the data and a brief description of the

five dc circuits. The rest of the section provides failure mode likelihood and duration information

based on specific parameters, as was done for the AC test data.

4.1 DC Data Analysis Approach

The analysis for the dc is discussed in this section. The data that was analyzed corresponds to

the experiments performed under the DESIREE-FIRE testing program [5]. For the intra-cable

experiments, there were five different circuit types (1-in Valve, Large Coil, motor-operated valve

(MOV), solenoid-operated valve (SOV), and switchgear (SWGR)); the analysis for each will be

discussed here in detail.

The dc data required additional review and processing to ensure a consistent method of

determining the specific failure points of concern. To accomplish this, threshold voltage levels

were identified for specific conductors that corresponded with a specific failure mode. This

information is presented below. These voltage levels were then used on the specific circuit data

to generate state diagrams, which present a clear view of the circuit status, gleaned from the

noisy data signals collected during testing. It was from these state diagrams that the failure

mode timelines and duration information were imported into the database. Each circuit is

discussed below, along with the criteria for evaluating each conductor for specific failure modes.

4.1.1 1-inch valve control circuit

The 1-inch valve circuit that was tested is shown below in Figure 4-1. As seen in the figure,

seven conductors were monitored during the test. From these seven conductors, the electrical

measurement data were analyzed based on the information displayed in Table 4-1 and Table

4-2 for the penlight and intermediate-scale tests, respectively. There is a slight difference in the

logic for the penlight and intermediate-scale tests, due to the fact that the switches (normally

4-2

open (NO) and normally closed (NC) contacts) on the G and R conductors had worn out during

the penlight tests. Thus, the switches were both physically wired closed for all the intermediatescale tests. This data processing effort has taken this into account.

For the 1-inch valve circuit, conductor S was the hot short (HS)/spurious operation (SA) target,

and conductors G and R were the HS targets for the penlight tests. For intermediate-scale

tests, conductor S was the HS/SA target, and conductors G and R were not used for fuse

status. The SP conductor was a non-energized target that could either short to the positive or

negative sides of the circuit for all tests. The other conductors were used to determine whether

a fuse had blown. Once the positive or negative fuse had blown, the durations for the HS

and/or HS/SA were assumed to be complete.

Figure 4-1. Line drawing of the DC-SIM panel layout for a 1-inch coil circuit

Note: The NO contact on the “R” conductors and the NC contact on the “G” conductor were

wired closed for all intermediate-scale tests.

P

G

R

S

N1

N2

A

V

5A

1-INCH

COIL

1750

+

-125 VDC

DCCCS CABLE UNDER TEST FROM DISTRIBUTION

CIRCUIT BREAKER

FUSE BLOCK

5A NC

NO

A

4-3

Table 4-1. Analysis logic for 1-in valve Penlight tests

Conductor

Spurious

Operation

(Status 2)

(Status 1)

Normal

(Status 0)

Fuse Clear or Spare

Conductor Short

(Status -1)

P VPModified>100V VPModified<10V

[Positive Fuse Clear]

G

S=2 &

VGModified>100V

[Hot Short]

VGModified>100V

R

S≠2 &

VRModified>100V

[Hot Short]

VRModified<10V

S

VSModified>48 V

[Hot Short-Induced

Spurious Operation]

VSModified<48 V

N1 VN1Modified<10V VN1Modified>100V

[Negative Fuse Clear]

N2 VN2Modified<10V VN2Modified>100V

[Negative Fuse Clear]

SP VSp Raw >30V

[Short to Positive]

VSpRaw ~ 0V VSp Raw <-30V

[Short to Negative]

Raw – voltage reference is ground Modified – voltage level is approximately battery negative

Table 4-2. Analysis logic for 1-in valve intermediate-scale tests

Conductor

Spurious

Operation

(Status 2)

(Status 1)

Normal

(Status 0)

Fuse Clear or Spare

Conductor Short

(Status - 1)

P VPModified>100V VPModified<10V

[Positive Fuse Clear]

G VGModified>100V VGModified<10V

[Positive Fuse Clear]

R VRModified>100V VRModified<10V

[Positive Fuse Clear]

S

VSModified>48 V

[Hot Short-Induced

Spurious Operation]

VSModified<48 V

N1 VN1Modified<10V VN1Modified>100V

[Negative Fuse Clear]

N2 VN2Modified<10V VN2Modified>100V

[Negative Fuse Clear]

SP VSp Raw >30V

[Short to Positive]

VSpRaw ~ 0V VSp Raw <-30V

[Short to Negative]

4-4

4.1.2 Large coil control circuit

The large coil circuit that was tested is shown below in Figure 4-2. As seen in the figure, there

are seven conductors that were monitored during the test. For those seven conductors, the

electrical measurement data was analyzed based on the information displayed in Table 4-3 for

all tests. For this, circuit conductor S was the HS/SA target, and conductor R was an HS target

for all tests. The SP conductor was a non-energized target that could either short to the positive

or negative sides of the circuit for all tests. The other conductors were used to determine

whether a fuse had blown. Once the positive or negative fuse had blown, the durations for the

HS and/or HS/SA were assumed to be complete.

Figure 4-2. Line drawing for the DC large coil circuit

P

G

R

S

N1

N2

A

V

10A

LARGE

COIL

1750

+

-125 VDC

DCCCS CABLE UNDER TEST FROM DISTRIBUTION

CIRCUIT BREAKER

FUSE BLOCK

10A

4-5

Table 4-3. Analysis logic for large coil Penlight and intermediate-scale tests

Conductor

Spurious

Operation

(Status 2)

(Status 1)

Normal

(Status 0)

Fuse Clear or Spare

Conductor Short

(Status - 1)

P VPModified>100V VPModified<10V

[Positive Fuse Clear]

G VGModified>100V VGModified<10V

[Positive Fuse Clear]

R VRModified>60V

[Hot Short]

VRModified<60V

S

VSModified>60 V

[Hot ShortInduced Spurious

Operation]

VSModified<60 V

N1 VN1Modified<10V VN1Modified>100V

[Negative Fuse Clear]

N2 VN2Modified<10V VN2Modified>100V

[Negative Fuse Clear]

SP VSp Raw >30V

[Short to Positive]

VSpRaw ~ 0V VSp Raw <-30V

[Short to Negative]

4.1.3 dc MOV control circuit

The MOV circuit that was tested is shown below in Figure 4-3. As seen in the figure, there are

seven conductors that were monitored during the test. Those seven conductors’ electrical

measurement data was analyzed based on the information displayed in Table 4-4 for all tests.

Each test had two MOV circuits designated as MOV1 and MOV2. Conductors YO1 and YC1 for

MOV1 were HS/SA and HS targets. With MOV1, there were mechanical interlocks that caused

YC1 to lock out if YO1 was engaged; thus, if YO1 had an HS/SA while YC1 got an HS, YC1

would not engage. Conductors G and R were HS targets. The SP conductor was a nonenergized target that could short to either the positive or the negative side of the circuit for all

tests. The other conductors were used to determine whether a fuse had blown. Once the

positive or negative fuse had blown, the durations for the HS and/or HS/SA were assumed to be

complete.

4-6

Figure 4-3. Line drawing for DC MOV circuit

Table 4-4. Analysis logic for MOV Penlight and intermediate-scale tests

Conductor

Spurious

Operation

(Status 2)

(Status 1)

Normal

(Status 0)

Fuse Clear or

Spare

Conductor

Short

(Status - 1)

G

VYO1Modified>100V

& VGModified>100V

VGModified>100V

N

VNModified<10V VNModified>100V

[Negative Fuse

Clear]

P VPModified>100V VPModified<10V

[Positive Fuse Clear]

R VYO1Modified>100V

& VRModified>100V

VRModified>100V

YC1 (MOV1) VYC1Modified>89.3V

& IYC1>0.06A

YO1=2 &

VYC1Modified>89.3V

VYC1Modified<10V &

VYO1Modified<10V

YC1 (MOV2) VYC1Modified>50.7V

& YO1 ≠ 2

YO1=2 &

VYC1Modified>50.7V

VYC1Modified<10V &

VYO1Modified<10V

YO1 (MOV1) VYO1Modified>29.0V

& IYO1>0.06A

YC1=2 &

VYO1Modified>29.0V

VYC1Modified<10V &

VYO1Modified<10V

YO1 (MOV2) VYO1Modified>50.7V

& IYO1>0.06A

YC1=2 &

VYO1Modified>50.7V

VYC1Modified<10V &

VYO1Modified<10V

SP VSp Raw >30V

[Short to Positive]

VSpRaw ~ 0V VSp Raw <-30V

[Short to Negative]

G

P

YC1

YO1

R

N

A

V

NC

1750

+

-125 VDC

O

NO

NC

C

A

1750

DCCCS CABLE UNDER TEST FROM DISTRIBUTION

CIRCUIT BREAKER

FUSE BLOCK

10A

A

B

C

4-7

4.1.4 Small pilot SOV control circuit

The SOV circuit that was tested is shown below in Figure 4-4. As seen in the figure, there are

seven conductors that were monitored during the test. Those seven conductors’ electrical

measurement data was analyzed based on the information displayed in Table 4-5 for all tests.

For this circuit conductor, S2 was the HS/SA target, and conductor R was an HS target for all

tests. The SP conductor was a non-energized target that could short to either the positive or the

negative side of the circuit for all tests. The other conductors were used to determine whether a

fuse had blown. Once the positive or negative fuse had blown, the durations for the HS and/or

HS/SA were assumed to be complete.

Figure 4-4. Line drawing for DC SOV circuit

S1

G

R

S2

N

A P

A

V

5A

SOV

1750

+

-125 VDC

DCCCS CABLE UNDER TEST

FROM DISTRIBUTION

CIRCUIT BREAKER

FUSE BLOCK

4-8

Table 4-5. Analysis logic for SOV penlight and intermediate-scale tests

Conductor

Spurious

Operation

(Status 2)

(Status 1)

Normal

(Status 0)

Fuse Clear or

Spare

Conductor

Short

(Status - 1)

P,G,S1 VModified>100V VModified<10V

[Positive Fuse Clear]

N VNModified<10V VNModified>100V

[Negative Fuse

Clear]

R VRModified>60V

[Hot Short]

VRModified<60V

S2 VS2Modified>56.05V VS2Modified<60V

SP VSp Raw >30V

[Short to Positive]

VSpRaw ~ 0V VSp Raw <-30V

[Short to Negative]

4.1.5 Medium-voltage circuit breaker dc control circuit

There were two different medium-voltage circuit breakers (SWGR) circuits used during

DESIREE testing. As mentioned in the report, there was a problem with the first breaker during

intermediate-scale Test #8. The first SWGR circuit is displayed in Figure 4-5, with the

instrumentation’s data analysis displayed in Table 4-6. The internal manufacturer wired this

SWGR in reverse, which is depicted in Figure 4-5. The wiring did not affect the functionality of

the SWGR, the only difference being that the red light was not energized. Table 4-6 has a

different set-up than the tables for the previous circuits analyzed. The SWGR circuits were

more complex to analyze, resulting in the different format. Conductors G, T, and C1 were hot

short targets, while T and C1 were used to determine whether the breaker had tripped or closed

(HS/SA target). The duration for the HS/SA was never more than one time step. Conductor R

was treated as a energized spare. The two SP conductors were non-energized targets that

could short to either the positive or the negative side of the circuit for all tests. The other

conductors were used to determine whether a fuse had blown. Once the positive or negative

fuse had blown, the durations for the HS and/or HS/SA were assumed to be complete. The

second SWGR circuit is displayed in Figure 4-6, with the instrumentation’s data analysis

displayed in Table 4-7. The only difference with this SWGR in terms of the data analysis logic

was that R was an HS target and not an energized spare. It is also noted in Table 4-6 and

Table 4-7 that there were two cables tested for each SWGR test. One cable was connected to

the close circuit, and the other was connected to the trip circuit. The conductors associated with

each are identified in the tables.

4-9

Figure 4-5. Line drawing for DC SWGR 1 circuit

4-10

Figure 4-6. Line drawing for DC SWGR 2 circuit

4-11

Table 4-6. Analysis logic for SWGR Penlight tests and intermediate-scale

Conductor Logic Statements (adjusted

voltage used) Notes

Close Cable

C1 If(VC1<10V, “EtC”, if(45V< VC1<75V,

“Floating,” if VC1>100V, “HS,” “HS or

Floating”))

EtC means enable to close. If a

fuse clears on the close circuit,

this conductor state becomes

Not_EtC (not enable to close).

HS means hot short.

PC If(VP>100V, “Normal,” “Pos. Fuse

Blown”)

N1 If(VN1<10V, “Normal,” “Neg. Fuse

Blown”)

Trip Cable

G If(VG<10V, “G_On”, “G_Off”) If the green light is off and T is

floating, then there is a hot

short.

R If(VR<60V, “HS,” “Normal”) Internal wiring was reversed; R

was treated as a hot spare.

PT If(VPT>100V, “Normal,” “Pos. Fuse

Blown”)

N2 If(VN2<10V, “Normal,” “Neg. Fuse

Blown”)

T If(VT<10V, “EtT”, if( VT>100V, “HS,”

“Floating”))

EtT means enable to trip. If a

fuse clears on the trip circuit, this

conductor state becomes

Not_EtT (not enable to trip).

SP1 If(VS1<30V, “Short_to_-,” If(VS1>90V,

“Short_to_+,” “Floating/Normal”))

SP2 If(VS2<30V, “Short_to_-,” If(VS1>90V,

“Short_to_+,” “Floating/Normal”))

Breaker Position Breaker position was determined by

analysis of the conductors’ behavior,

as well as of the experimental field

notes. This was necessary because

of the interdependencies between

the trip and close circuits.

4-12

Table 4-7. Analysis logic for SWGR intermediate scale tests 1, 3, 5, 6, 7, 8, 9, 10, Cont.

1, and Cont. 2

Conductor If Statements (adjusted voltage

used) Notes

Close Cable

C1 If(VC1<10V, “EtC,” if(45V<

VC1<75V, “Floating,” if VC1>100V,

“HS,” “HS or Floating”))

EtC means enable to close. If a

fuse clears on the close circuit, this

conductor state becomes Not_EtC

(not enable to close). HS means

hot short.

PC If(VP>100V, “Normal,” “Pos. Fuse

Blown”)

N1 If(VN1<10V, “Normal,” “Neg. Fuse

Blown”)

Trip Cable

G If(VG<10V, “G_On,” “G_Off”) If the green light is off and T is

floating, then there is a hot short.

R If(VR<10V, “R_On,” “R_Off”) If the red light is on and T is floating,

then there is a hot short.

PT If(VPT>100V, “Normal,” “Pos. Fuse

Blown”)

N2 If(VN2<10V, “Normal,” “Neg. Fuse

Blown”)

T If(VT<10V, “EtT,” if( VT>100V,

“HS,” “Floating”))

EtT means enable to trip. If a fuse

clears on the trip circuit, this

conductor state becomes Not_EtT

(not enable to trip).

SP1 If(VS1<30V, “Short_to_-,”

If(VS1>90V, “Short_to_+,”

“Floating/Normal”))

SP2 If(VS2<30V, “Short_to_-,”

If(VS1>90V, “Short_to_+,”

“Floating/Normal”))

Breaker Position Breaker position was determined

by analysis of the conductors’

behavior, as well as of the

experimental field notes. This

was necessary because of the

interdependencies between the

trip and close circuits.

4-13

4.2 Conductor Count

The test data used to evaluate the effect cable conductor count has on failure modes included

multi-conductor cables with 2-6, 7-9, and 10-15 conductors. Table 4-8 provides summaries of

the dc test data, separated into these three conductor count ranges. These ranges were

suggested by the electrical Phenomena Identification and Ranking Table (PIRT) expert panel.

Figure 4-7 provides a graphical representation of this data.

Table 4-8. Conductor count, global approach, DC tests

Global Approach 1/C 2-6/C 7-9/C 10-15/C >15/C

Fuse Clear - 1 22 1 -

Hot Short - 4 142 5 -

Spurious Operation - 3 89 2 -

HS/SO Possible - 5 164 6 -

Figure 4-7. Conductor count column plot, global approach, DC tests

These fire-induced cable failure mode plots provide little insight into how conductor count affects

the likelihood of any one failure mode. This is partially due to the abundance of conductor count

data available for 7/C cables, as well as the fact that the data shows consistent results among

the three bins even with minimal data for the other two bins. Table 4-9 and Figure 4-8 provide

dc test data for hot short and spurious operation durations, separated by these same conductor

count ranges.

1/C 2-6/C 7-9/C 10-15/C >15/C

Count

0

50

100

150

200

Fuse Clear

Spurious Operation

HS/SO Possible

100%

54%

87%

20%

80%

60%

100%

13%

17%

83%

33%

4-14

Table 4-9. Conductor count, duration data, DC tests

Hot Short Spurious Operation

1/C 2-6/C 7-9/C 10-15/C >15/C 1/C 2-6/C 7-9/C 10-15/C >15/C

q1 - 101.5 14 18 - - 203.5 10 105 -

min - 1 1 7 - - 193 1 105 -

median - 193 47 63 - - 214 31 105 -

max - 1082 8545 2873 - - 235 6417 105 -

q3 - 265 254 242 - - 224 80 105 -

mean - 302 409 471 - - 214 195 105 -

Figure 4-8. Conductor count box plot, duration, DC tests

4.3 Thermal Exposure Conditions

This section presents the dc data evaluated by thermal exposure conditions’ effects on fireinduced failure modes. The thermal exposure conditions include flame, hot gas layer (HGL),

plume, and radiant conditions. The flame, hot gas layer, and plume data are from the

intermediate-scale testing, while the radiant test data are from the Penlight (small-scale) radiant

testing. These thermal exposure conditions are discussed in more detail in Section 2.3. Table

4-10 provides summaries of the dc test data failure mode evaluation by thermal exposure

conditions, while Figure 4-9 presents this information graphically.

0

50

100

150

200

250

300

350

400

450

500

2‐6/C 7‐9/C 10‐15/C 2‐6/C 7‐9/C 10‐15/C

Hot Short SpuriousOperation

q1

min

median

max

q3

1082s 8545s 2873s 6417s

4-15

Table 4-10. Thermal exposure conditions, global approach, DC tests

Global Approach Flame Plume HGL Radiant

Fuse Clear 9 3 5 7

Hot Short 43 25 13 70

Spurious Operation 26 11 5 52

HS/SO Possible 52 28 18 77

Figure 4-9. Thermal exposure conditions column plot, global approach, DC tests

The failure mode data indicates that the HGL exposure data is an outlier compared to the other

exposure conditions. The HGL test data shows a lower likelihood of experiencing a spurious

operation (28%) and a higher chance of having the circuit protective fusing clear (28%). It is

interesting to note that it was believed that the Penlight radiant exposure simulated an HGL

exposure, due to the high radiative heat transfer that occurs in a sooty HGL. This assumption

may be accurate for comparisons of the thermal conditions, but the failure mode data does not

show this relation. This data tends to indicate that fire-induced cable failure modes do not follow

this same logic, and, more specifically, that the radiant failure mode likelihood data is similar to

the plume and flame exposure condition failure mode results. This may be due to the high

intensity of the radiant exposure.

Table 4-11 and Figure 4-10 present the dc test’s hot short and spurious operation duration data,

separated by thermal exposure conditions. The data shows a weak trend (based on the median

of the data) for shorter duration hot shorts in flame and radiant exposures as opposed to HGL

exposure, with the plume exposure durations lying somewhere in the middle. There is a similar

trend in the AC test data results (Section 2.3).

Flame Plume HGL Radiant

Count

0

20

40

60

80

100

Fuse Clear

Spurious Operation

HS/SO Possible

100%

39%

89%

11%

100%

50%

83%

17%

100%

28%

78%

28%

100%

68%

91%

9%

4-16

Table 4-11. Thermal exposure conditions, duration data, DC tests

Hot Short Spurious Operation

Flame Plum

e

HGL Radiant Flame Plume HGL Radiant

q1 16.4 27.5 57.95 12 13 10.7 34.8 10

min 2 2 7 1 3 3.4 26 1

median 40 154 115 43 34 20.6 70 31

max 2873 2590 4871 8545 124 198.4 115 6417

q3 119.2 740 714 210 66.7 60.5 90.0 98.3

mean 61.6 468.7 587.8 428.4 45.1 146.6 111.9 301.0

Figure 4-10. Thermal exposure conditions box plot, duration, DC tests

4.4 Raceway Routing

The two raceway routing configurations used during testing were open ladder-back cable trays

and rigid steel conduit configurations that were tested in DESIREE-FIRE. The dominant use of

ladder-back cable tray configurations makes it difficult to determine the effects that these

configurations have on cable failure. A summary of these results is shown in Table 4-12 and

Figure 4-11. The data evaluated shows no difference in failure mode between cable tray and

conduit configurations for dc circuits.

Table 4-12. Raceway routing, global approach, DC tests

Global Approach Conduit Tray

Fuse Clear 4 20

Hot Short 18 133

Spurious Operation 13 81

HS/SO Possible 22 153

0

100

200

300

400

500

600

700

800

Flame Plume HGL Radiant Flame Plume HGL Radiant

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

2873s 2590s 8545s 4871s 6417s

4-17

Figure 4-11. Raceway routing column plot, global approach, DC tests

Table 4-13 and Figure 4-12 present the data that was evaluated for raceway routing against hot

short and spurious operation durations. The interquartile range, shown in Figure 4-12, is wider

for the hot short durations than for the spurious operation durations, with the median for hot

shorts being about 13-17 seconds longer.

Table 4-13. Raceway routing, duration data, DC data

Hot Short Spurious Operation

Conduit Tray Conduit Tray

q1 14.1 16.0 16.4 10.0

min 1 1 3 1

median 56 50 39 33.5

max 2804 8545 431 6417

q3 278.5 255 87 90

mean 405.8 408.8 80.8 212.0

Figure 4-12. Raceway routing box plot, duration, DC tests

CONDUIT TRAY

Count

0

20

40

60

80

100

120

140

160

180

Fuse Clear

Spurious Operation

HS/SO Possible

100%

14%

86% 68% 13%

87%

53%

0

100

200

300

400

500

CONDUIT TRAY CONDUIT TRAY

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

2804s 6417s 8545s

4-18

4.5 Cable Orientation

DESIREE-FIRE only tested cables in the horizontal orientation; thus, no comparison can be

made on this parameter for dc circuits.

4.6 Raceway Fill

The dc test data was evaluated based on the raceway fill conditions (single, medium,

partitioned) and their effect on the failure mode. The single cable raceway fill configurations are

shown below in Figure 4-13. Most of this single-fill data came from the Penlight tests, with a few

data points coming from the intermediate-scale tests. If two single cables were in a raceway

(e.g., Figure 4-14, Fill Tray H), it was also considered a single cable fill. Cables next to a

partitioned cable group but separate (e.g., Bundle Trays D & H), as shown in Figure 4-15 with

the single cable off to the right, were also considered single cables for this specific analysis.

Besides the few instances mentioned above, all fill trays represented in Figure 4-14 and Figure

4-16 were analyzed as medium-fill, and the fill trays represented in Figure 4-15 were analyzed

as partitioned cable tray raceway fill. In Section 2.6, bundles represent cable groups held

together by tie wraps. Tie wraps were not used in the dc testing to group cables together;

instead, thin steel right-angle plates were connected to the cable tray rungs.

Figure 4-13. Circuit cable orientation within the cable trays for single fill

4-19

Figure 4-14. Circuit cable orientation for filled trays

Tray Fill A Tray Fill B

Tray Fill C Tray Fill D

Tray Fill E Tray Fill F

Tray Fill G Tray Fill H

4-20

Figure 4-15. Circuit cable orientation for partitioned trays

4-21

Figure 4-16. Circuit cable orientation for specialized trays

Table 4-14 provides summaries of the dc failure mode test data, separated by raceway fill type.

The graphical representation of this data is shown in Figure 4-17. As shown in these figures,

there is not a significant effect on failure modes based on raceway fill configurations. One

observation of note is the slightly lower likelihood of experiencing a spurious operation in the

partitioned tray configuration. However, this was not observed in the medium-full

configurations, making it difficult to explain this result as the shielding effect of the other cables

surrounding the monitored cables.

Table 4-14. Raceway fill, global approach, DC tests

Global Approach Partitioned Medium Single

Fuse Clear 8 6 10

Hot Short 35 39 77

Spurious Operation 16 21 57

HS/SO Possible 43 45 87

Figure 4-17. Raceway fill column plot, global approach, DC tests

1 2 TC 3 4

Specialized Tray

A

1 TC 2

3 TC 4 TC

Specialized Tray

B

1 TC 2 TC 3 TC

Specialized Tray

C

Partitioned Medium Single

Count

0

20

40

60

80

100

Fuse Clear

Spurious Operation

HS/SO Possible

100%

37%

81%

19%

13%

87%

47%

11%

66%

89%

4-22

The duration data was also evaluated against the raceway fill configurations. The analysis

results are shown below in Table 4-15 and Figure 4-18. No trend was identified for the duration

data based on raceway fill.

Table 4-15. Raceway fill, duration data, DC tests

Hot Short Spurious Operation

Bundle Medium Single Bundle Medium Single

q1 31 17.6 12.6 14.4 13 10.2

min 2 2 1 3 2 1

median 115 42 46 34 35 31

max 4871 2873 8545 198 124 6417

q3 675 124 240.5 73.6 82.5 97.2

mean 530 219 444 53 47 289

Figure 4-18. Raceway fill box plot, duration, DC tests

0

100

200

300

400

500

600

700

Bundle Medium Single Bundle Medium Single

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

4871s 8545s 6417s

4-23

4.7 Insulation Type

The insulation type parameter separates insulation materials into two categories of polymer

types, thermoset (TS) and thermoplastic (TP). Table 4-16 provides a breakdown of how

insulation materials are classified by insulation type. Table 4-17 and Figure 4-19 present the

failure mode test data separated by cable conductor insulation type, TS and TP. Section 4.8

provides information on failure characteristics based on insulation materials, and Section 4.9

presents the data segregated by insulation and jacket type combinations.

Table 4-16. Breakdown of insulation material by type, DC tests

Thermoset Materials (TS) Thermoplastic Materials (TP)

EPR – ethylene propylene rubber PE – polyethylene

FR-Kerite – Flame Retardant Kerite™ PVC – polyvinyl chloride

XLPE – cross-linked polyethylene TEF – Tefzel

XLPO – cross-linked polyolefin

Table 4-17. Insulation type, global approach, DC tests

Global Approach TP TS

Fuse Clear 16 7

Hot Short 48 99

Spurious Operation 36 55

HS/SO Possible 64 106

Figure 4-19. Insulation type column plot, global approach, DC tests

The data indicates that insulation type has little effect on the likelihood of spurious operation, but

has a minor effect on the likelihood of experiencing a fuse clear failure. Here the TS insulation

has a lower likelihood of experiencing a fuse clear (7%), and, thus, a higher likelihood of

experiencing a hot short than a TP-insulated cable. Once again, as was shown in the AC test

results, there is no difference between cable insulation types relative to the likelihood of

experiencing a spurious operation.

TP TS

Count

0

20

40

60

80

100

120

Fuse Clear

Spurious Operation

HS/SO Possible

100%

25%

75%

56%

7%

93%

52%

4-24

The insulation type data was used to determine its effect on failure mode durations, which is

shown below in Table 4-18 and Figure 4-20. The TP-insulated cables showed slightly longer

hot short and spurious operation duration, based on the median and inter-quartile range.

Table 4-18. Insulation type, duration data, DC tests

Hot Short Spurious Operation

TP TS TP TS

q1 23.3 12.8 27.5 5.0

min 1 1 1 1

median 79 42 90 22

max 6417 8545 6417 1195

q3 372.8 212.2 142.6 36.8

mean 476 376 420 57

Figure 4-20. Insulation type box plot, duration, DC tests

4.8 Insulation Material

The next cut-set evaluates the different types of cable insulation materials. The cable insulation

materials used during the dc testing were ethylene propylene rubber (EPR), cross-linked

polyethylene (XLPE), flame-retardant kerite™ (FR-Kerite), polyethylene (PE), polyvinyl chloride

(PVC), and Tefzel™ (TEF), which can also be separated into TS and TP materials. These

materials were analyzed for a better understanding of their effects on cable failure modes, as

shown in Table 4-19. This data is presented graphically in Figure 4-21. The data suggests that

conductors insulated with PE or PVC have a higher likelihood (20% and 17%, respectively) of

experiencing a fuse clear failure than the other materials. It is interesting to note that both PE

and PVC are TP materials, and that TEF, another TP material, experienced zero fuse clear

failures, while the TS material also experienced a low number of fuse clear failures (~6%).

0

100

200

300

400

500

TP TS TP TS

Hot Short SpuriousOperation

Duration

q1

min

median

max

q3

6417s 1195s 8545s 6417s

4-25

Table 4-19. Insulation material, global approach, DC tests

Global Approach TS TP

EPR XLPE FR-Kerite PE PVC TEF

Fuse Clear 1 4 1 15 1 0

Hot Short 17 66 15 35 5 8

Spurious Operation 5 41 8 26 4 6

HS/SO Possible 18 70 16 50 6 8

Figure 4-21. Insulation material column plot, global approach, DC tests

This data set was analyzed with the failure durations summarized in Table 4-20 and displayed in

Figure 4-22. The data shows that the PVC- and EPR-insulated cables have a very short

duration; however, only a limited number of PVC cables were tested (6 total).

Table 4-20. Insulation material, duration data, DC tests

Hot Short Spurious Operation

TS TP TS TP

EPR XLPE PE PVC TEF EPR XLPE PE PVC TEF

q1 7.3 12.3 33.9 1.3 17 3.9 10 28 1 425

min 1 1 1 1 2 3 1 10 1 91

median 53 38 95 13 72 5 23 90 1 759

max 724 4871 6417 84 1433 34 115 6417 1 1427

q3 149 115 676 28.8 290 9.5 37 124 1 1093

mean 146 289 575 22 293 10 28 409 1 759

EPR XLPE FR-Kerite PE PVC TEF

Count

0

20

40

60

80

Fuse Clear

Spurious Operation

HS/SO Possible

100%

28%

94%

6%

94%

59%

6%

94%

50%

30%

70%

52%

17%

83%

67%

100%

75%

0%

4-26

Figure 4-22. Insulation material box plot, duration, DC tests

4.9 Insulation-Jacket Type Combinations

The test data was next evaluated based on the combination of cable insulation and jacket types.

There are three combinations identified from the data, namely (1) thermoplastic-insulated,

thermoplastic-jacketed, (2) thermoset-insulated, thermoset-jacketed, and (3) thermosetinsulated, thermoplastic-jacketed. Table 4-21 provides summaries of the dc test data, divided

into these three categories. This information is displayed in column plots in Figure 4-23, which

shows that when TS-TS cables are compared to TP-TP cables, the failure mode likelihood data

is similar to the results obtained from the comparison of the insulation type. It is probable and

logical that insulation material is the dominant influencing factor for the failure mode likelihood.

The TS-TP category comprises a single cable type, namely, the armored cable provided

through the NRC-RES/EPRI Memorandum of Understanding (MOU). The failure modes show a

high likelihood of experiencing a spurious operation and hot short. These results are consistent

with industry testing of armored cable. The high percentage of spurious operation and hot

shorts is a result of an ungrounded power supply and electrical interactions with the armor

during fire-induced failure.

Table 4-21. Insulation-jacket type, global approach, DC tests

Global Approach TP-TP TS-TS Armored (TS-TP)

Fuse Clear 16 6 0

Hot Short 48 70 12

Spurious Operation 36 41 9

HS/SA Possible 64 76 12

0

200

400

600

800

1000

1200

EPR XLPE PE PVC TEF EPR XLPE PE PVC TEF

TS TP TS TP

Hot Short SpuriousOperation

Secnods

q1

min

median

max

q3

4871s 6417s 6417s 1427s 1433s

4-27

Figure 4-23. Insulation-jacket type column plot, global approach, DC tests

The durations for the hot shorts and spurious operations for the jacket types were evaluated

using the global approach. The data is presented in Table 4-22 with the box plots shown in

Figure 4-24. Similar to what was shown in the insulation type analysis of Section 4.7, the TP-TP

material cables show longer duration than the TS-TS cables. The mechanism for this

phenomenon is unclear to the authors, but it may be the insulation polymer material’s sequence

of physical thermal degradation.

Table 4-22. Insulation-jacket type, duration data, DC tests

Hot Short Spurious Operation

TP-TP TS-TS Armored (TS-TP) TP-TP TS-TS Armored (TS-TP)

q1 23.3 14 19.8 27.5 9 4.8

min 1 1 1 1 1 4

median 79 42 39 90 24 21

max 6417 8545 2590 6417 1195 42

q3 372.8 255.8 182 142.6 37 37.5

mean 476 429 298 420 73 22

TP-TP TS-TS Armored (TS-TP)

Count

0

20

40

60

80

100

Fuse Clear

Spurious Operation

HS/SO Possible

100%

25%

75%

56%

8%

92%

54%

100%

0%

100%

75%

100%

4-28

Figure 4-24. Insulation-jacket type box plot, duration, DC tests

4.10 Wiring Configuration

The test data used to evaluate the wiring configuration effects on failure modes included five

types of configurations. These configurations are shown in Table 4-23, identifying the number

of source, target, and common return conductors within a test cable, along with the associated

circuit type.

Table 4-23. DC test data wiring configurations

Sources # Targets # Returns dc Circuit

Configuration 1 2 4 1 MOV

Configuration 2 2 3 1 N/A

Configuration 3 2 2 1 N/A

Configuration 4 3 3 1 SOV

Configuration 5 2 3 2 1-IN & LG COIL

Configuration 6 1 1 1 SWGR - C

Configuration 7 1 5 1 SWGR - T

Table 4-24 provides summaries of the dc test data, divided into the different types of

configurations. This information is shown graphically in Figure 4-25. Configuration 6 had zero

fuse clears, and configuration 7 had the highest percentage of fuse clears. Configuration 1 had

the highest percentage (61%) of spurious operations, while configuration 6 had the lowest

(41%). Configuration 7 had the lowest percentage of hot shorts (65%), as well as the lowest

source-to-target ratio (1:5).

0

100

200

300

400

500

TP‐TP TS‐TS Armored (TS‐TP) TP‐TP TS‐TS Armored (TS‐TP)

Hot Short SpuriousOperation

q1

min

median

max

q3

6417s 8545s 6417s 2590s 1195s

4-29

Table 4-24. Wiring configuration, global approach, DC tests

Global Approach Config. 1 Config. 4 Config. 5 Config. 6 Config. 7

Fuse Clear 4 7 5 0 8

Hot Short 50 35 29 22 15

Spurious Operation 33 19 19 9 14

HS/SO Possible 54 42 34 22 23

Figure 4-25. Wiring configuration column plot, global approach, DC tests

This data set was analyzed to determine wiring configuration influence on hot short duration.

This is shown below in Table 4-25 and Figure 4-26. It should be noted that the durations for

spurious operations for configurations 6 and 7 are not calculated, as mentioned above. Since

these are the close and trip circuits of the switchgear, the duration is less than a second, and is

never continuous; therefore, it is not relevant to this analysis. Configuration 6 had a significantly

longer median for hot short duration.

Table 4-25. Wiring configuration, duration data, DC tests

Config. 1 Config. 4 Config. 5 Config. 6 Config. 7

q1 11 17.5 13.2 35.2 8.9

min 1 1 1 2 1

median 37 59 46.5 176 76

max 8545 724 1143 4871 1397

q3 173.2 96.2 121.8 1085.8 709

mean 405 110 195 736 351

Spurious Operation

Config. 1 Config. 4 Config. 5 Config. 6 Config. 7

q1 10.8 23 7 N/A N/A

min 1 3 1 N/A N/A

median 33.5 37 13 N/A N/A

max 6417 198.4 1052 N/A N/A

q3 96.0 69.6 90 N/A N/A

mean 286 53 129 N/A N/A

Config. 1 Config. 4 Config. 5 Config. 6 Config. 7

Count

0

10

20

30

40

50

60

Fuse Clear

Spurious Operation

HS/SO Possible

100%

61%

93%

7%

17%

83%

45%

15%

85%

56%

0%

100%

41%

65%

61%

35%

4-30

Figure 4-26. Wiring configuration box plot, duration, DC tests

4.11 Conductor Size

The test data was used to evaluate the effect that conductor size has on failure modes (12 AWG

vs. 14 AWG). Table 4-26 provides summaries of the dc test data, divided into the different

conductor sizes. The majority of the test data is for 12 WG cables, with only 8% being of the 14

AWG variety. The global approach does not result in any significant differences among failure

modes as a result of cable conductor size. Figure 4-27 provides the graphical representation of

the failure mode characteristics for cable conductor size.

Table 4-26. Conductor size, global approach, DC tests

Global Approach 12 AWG 14 AWG

Fuse Clear 23 1

Hot Short 138 13

Spurious Operation 86 8

HS/SA Possible 161 14

0

400

800

1200

1600

Config. 1 Config. 4 Config. 5 Config. 6 Config. 7 Config. 1 Config. 4 Config. 5 Config. 6 Config. 7

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

8537s 4871s 6417s

4-31

Figure 4-27. Conductor size column plot, global approach, DC tests

Table 4-27 and Figure 4-28 display the data that was analyzed based on conductor size for

failure mode durations. The data shows that the 14 AWG cables experience longer-lasting hot

shorts and spurious operations, which is based on a limited set of data for the 14 AWG cables.

Table 4-27. Conductor size, duration data, DC tests

Hot Short Spurious Operation

12 AWG 14 AWG 12 AWG 14 AWG

q1 14 20.8 11 15.5

min 1 1 1 1

median 47 194 33 193

max 6417 8545 6417 1195

q3 211.2 898.5 80 270.5

mean 355 965 186 280

Figure 4-28. Conductor size box plot, duration, DC tests

12 AWG 14 AWG

Count

0

20

40

60

80

100

120

140

160

180

Fuse Clear

Spurious Operation

HS/SO Possible

100%

14%

86%

100%

7%

93%

57%

53%

0

200

400

600

800

1000

1200

1400

12 AWG 14 AWG 12 AWG 14 AWG

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

6417s 6417s 8545s

4-32

4.12 Circuit Type

This cut-set separates the test data by circuit type (MOV, SOV, SWGR, 1-inch, and Large Coil).

These circuits are explained above in Section 4.1. Table 4-28 presents the data for the circuit

type’s effect on failure mode occurrence. Figure 4-29 presents this data graphically.

The MOV and 1-inch valve circuits show a higher likelihood for spurious operation at 76% than

the SOV, switchgear, and large coil circuit at 55%, 51%, and 53%, respectively. No specific

mechanism for this has been identified. Circuit type has no significant bearing on the likelihood

of fuse clears and hot shorts.

Table 4-28. Circuit type, global approach - DC tests

Global Approach MOV SOV SWGR 1-inch Large Coil

Fuse Clear 4 7 8 2 3

Hot Short 50 35 37 15 14

Spurious Operation 33 19 23 12 7

HS/SO Possible 54 42 45 17 17

Figure 4-29. Circuit type column plot, global approach, DC tests

The circuit types were also evaluated to determine whether circuit type had an effect on failure

mode durations. This information is displayed below in Table 4-29 and Table 4-30, and is

shown graphically in Figure 4-30. It should be noted that in Table 4-30 the duration for SWGR

spurious operations were not analyzed for this data set because the duration of a breaker

tripping or closing in only about one time step in data collection would skew the duration data.

Hot short duration is unaffected by the circuit design, and the durations of hot shorts have been

reviewed. The switchgear and large coil circuits have the longest median hot short durations

(136.5s and 71.5s respectively). The large coil has the longest median spurious operation

duration (52s), while the 1-inch coil has the shortest median spurious operation duration (13s).

No specific mechanism for this has been identified.

MOV SOV SWGR 1-Inch Large Coil

Count

0

20

40

60

Fuse Clear

Spurious Operation

HS/SO Possible

100%

61%

93%

7%

17%

83%

45%

18%

82%

51%

12%

88%

71%

18%

82%

41%

4-33

Table 4-29. Circuit type hot short only, duration data, DC tests

MOV SOV SWGR 1-inch Large Coil

q1 11 17.5 32.2 11.0 21.5

min 1 1 1 1 3

median 37 59 136.5 33 75.5

max 8545 724 4871 855 1143

q3 173.2 96.2 1082.8 91.5 124

mean 405 110 695 154 239

Table 4-30. Circuit type spurious operation only, duration data, DC tests

Spurious Operation

MOV SOV SWGR 1-inch Large Coil

q1 10.8 23 N/A 9.8 4.3

min 1 3 N/A 1 3

median 33.5 37 N/A 12.5 90

max 6417 198.4 N/A 811 1052

q3 96 69.6 N/A 37.2 111

mean 286 53 N/A 90 197

Figure 4-30. Circuit type box plot, duration, DC tests

0

200

400

600

800

1000

1200

1400

MOV SOV SWGR 1‐Inch Large Coil MOV SOV SWGR 1‐Inch Large Coil

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

8545s 4871s 6417s

4-34

4.13 Fuse Size

The effects of fuse size on failure mode likelihood and duration were evaluated at the request of

the PIRT panel. Although this evaluation only slightly differentiated the data from the previous

evaluation based on the circuit type, the PIRT panel thought that the effects of fuse size on

failure mode and duration could be significant and warranted an evaluation here. The dc testing

data is the only data that was binned by fuse size, and there were four (4) fuse sizes used in the

circuits tested in the dc testing program (DESIREE-FIRE). Table 4-31 presents the failure mode

data, and Figure 4-31 presents the information from the tables in column plots.

The data for the 35A and 15A fuse bins are entirely from the switchgear circuit and the trip and

close portions of that circuit, respectively. The 35A bin is an outlier, based on its lack of fuse

clear failures and lower likelihood of spurious operation (41%). The lack of fuse clear failures is

likely a result of finite insulation impedance during fire-induced failures, limiting the fault current

enough that it doesn’t exceed the fuse clear limits.

Table 4-31. Fuse size, global approach, DC tests

Global Approach 35A 15A 10A 5A

Fuse Clear 0 8 7 9

Hot Short 22 15 64 50

Spurious Operation 9 14 40 31

HS/SO Possible 22 23 71 59

Figure 4-31. Fuse size column plot, global approach, DC tests

The effects of fuse size on duration are presented in Table 4-32, and a box plot is provided in

Figure 4-32 to graphically illustrate this information. There is a clear trend (based on median

and inter-quartile range) indicating that, as the fuse size decreases, so does the duration of the

hot shorts and spurious operations.

35A 15A 10A 5A

Count

0

20

40

60

80

Fuse Clear

Spurious Operation

HS/SO Possible

100%

41%

100%

0%

35%

65%

61%

10%

90%

56%

85%

53%

15%

100%

4-35

Table 4-32. Fuse size, duration data, DC tests

Hot Short Spurious Operation

35A 15A 10A 5A 35A 15A 10A 5A

q1 35.2 8.9 12 12.3 N/A N/A 10 12

min 2 1 1 1 N/A N/A 1 1

median 176 76 42 43 N/A N/A 36 33

max 4871 1397 8545 855 N/A N/A 6417 811

q3 1085.8 709 171.8 96 N/A N/A 98.5 64

mean 736 351 382 123 N/A N/A 273 68

Figure 4-32. Fuse size box plot, duration, DC tests 4.14 Cable Shielding

This section evaluates the effect a cable shield has on the failure modes of electrical cables

exposed to damaging thermal conditions. The data that represents the cable shield category is

from two different cables. The first is a cable donated to the testing program by JNES. The

shield in this cable is described in NUREG/CR-7100:

“The cable included a spiral-wound copper shield wrap approximately 0.23 mm

(0.009 in) thick. Both inside and outside this shield wrap was a counter-wrapped

thin natural fiber fabric strip (e.g., a cotton canvas type material).”

The other shield-wrapped cable was a FR-Kerite insulated cable with a zinc shield wrap,

described in NUREG/CR-7102 as follows:

“A zinc tape is spiral-wound directly beneath the jacketing material and two fabric

wraps separate the insulated conductors from the zinc material.”

‐100

100

300

500

700

900

1100

1300

1500

35A 15A 10A 5A 35A 15A 10A 5A

Hot Short SpuriousOperation

Seconds

q1

min

median

max

q3

4871s 8545s 6417s NotApplicable NotApplicable

4-36

Thus, these two cable constructions represent shield wraps with substantial physical

characteristics and not shield wraps made from aluminized Mylar, a shield wrap commonly

found in instrumentation cable noise reduction. Also, this section is only intended to evaluate

the shield, and all armored cable data has been removed from this analysis. Table 4-33 and

Figure 4-33 present the failure mode likelihood data in tabular and graphical form. The results

of this analysis show no significant difference for the global approach based on cable shielding.

Table 4-33. Cable shielding, global approach, DC tests

Global Approach Shield No Shield

Fuse Clear 2 22

Hot Short 10 141

Spurious Operation 6 88

HS/SO Possible 12 163

Figure 4-33. Cable shielding column plot, global approach, DC tests

The effects of shielding on hot short durations are presented below in Table 4-34 and Figure 4-

34. This comparison doesn’t present any characteristics that differentiate the length of hot short

durations among cables with or without shields.

Table 4-34. Cable shielding, duration data, DC tests

Hot Short Spurious Operation

Shield No Shield Shield No Shield

q1 18 14 80.9 10.8

min 1 1 9 1

median 161 47 149 32

max 2873 8545 235 6417

q3 268.5 252 203.5 82.5

mean 398 409 135 198

Shield No Shield

Count

0

20

40

60

80

100

120

140

160

180

Fuse Clear

Spurious Operation

HS/SO Possible

100%

17% 83% 50%

13%

87%

54%

4-37

Figure 4-34. Cable Shielding box plot, duration, DC tests 4.15 DC Concurrence of Hot Short-Induced Spurious Operations

Concurrence of hot short-induced spurious operations, as discussed in this report, occurs when

more than one circuit (or cable) experiences individual hot shorts at the same time (i.e.,

concurrence). The intermediate-scale tests performed in DESIREE-FIRE consisted of 12 tests,

which included six to seven DC circuits per test. This section documents how the test results

were analyzed to identify times when hot short-induced spurious operations occurred

concurrently.

The DESIREE-FIRE project tested five different types of dc surrogate circuits: solenoidoperated valves (SOVs), motor-operated valves (MOVs), 1-inch valve solenoids, large coils

similar in size to a power-operated relief valve, and a medium-voltage circuit breaker, referred to

as switchgear (SWGR). The testing included two SOV and two MOV circuits, resulting in a total

of eight circuits (SOV-1, SOV-2, MOV-1, MOV-2, 1-inch valve, large coil, and switchgear trip

and close circuits). Most circuits were included in every intermediate-scale test. Since the

intermediate-scale tests have the most realistic fire exposure conditions, this information has the

most applicability to plant configuration, and is the focus of this discussion.

Two approaches were taken to evaluate the concurrence of the DC data set. The first approach

evaluates the DC data set for concurrence of spurious operations within a single test. The

second approach is identical to what was done for the AC results and evaluates the data from

all tests, but within specific fire exposure locations. Note that the draft version of this report only

evaluated the former, and a public comment received on that draft noted the value of performing

a similar analysis of the DC data for comparison purposes. This analysis has been added to the

final report and is presented at the end of this section, following the analysis of concurrence

among individual DC tests.

0.0

100.0

200.0

300.0

400.0

500.0

Shield No Shield Shield No Shield

Hot Short Spurious Actuation

Duration

q1

min

median

max

q3

2873s 6417s 8545s

4-38

Analysis of spurious operation concurrence within individual tests

Table 4-35 presents a listing of the four tests in which concurrent spurious operations occurred.

Although all concurrences occurred between cables of the same insulation type, the testing

configurations only tested one cable type per test; thus, the possibility of concurrence among

different cable insulation types was never present.

Table 4-35. Listing of concurrent spurious operations during intermediate-scale DC

testing (concurrences that occurred during an individual test)

Test #

Circuit

Experiencing

Concurrent SO

Duration of

individual SO

(seconds)

Duration of

Concurrent

SO (seconds)

Cable

Physical

Location

Cable

Insulation

Type

5 SOV-2

SOV-1

211

12 3 D

B in Conduit

5 SOV-2

DC MOV-1 Open

211

16 16 D

B in Conduit

6 1-inch valve

SWGR-Close

89

1 1 C

B in Conduit

6 1-inch valve

SWGR-Trip

89

1 1 C

B in Conduit

8 Large coil

SOV-1

123

90 90 A

A

8 Large coil

DC MOV-1 close

123

95 9 A

A

9 SOV-1

DC MOV-1 close

112

7 7 B

B

TS

9 SOV-1

DC MOV-1 close

112

1 1 B

B

TS

The following discussion provides additional information related to the individual concurrent hot

shorts in each test identified in Table 4-35. The plots that follow identify the circuit, times of

failure, and concurrence duration of the hot short. The figures show the start of a hot short,

represented as a diamond, while the squares indicate the end and the black lines represent the

duration of a hot short. The information on the horizontal axis of the figure indicates the circuitnaming convention:

 test series (D = DESIREE)

 testing scale (IT = Intermediate)

 test number

 the circuit that experienced the hot short

4-39

Figure 4-35. Time plot of concurrent hot shorts for DESIREE-FIRE

intermediate-scale test 5

Figure 4-35 depicts the DC hot short concurrence between SOV-2, SOV-1, and MOV-1 for

intermediate-scale Test #5. It is important to note the physical location of the cables because

thermal exposure conditions can influence the timing of cable failure. The SOV-2 cable is

located in position D (upper plume), while the SOV-1 and MOV-1 cables are both located in a

conduit in position B (lower plume). As referenced in Table 4-35, SOV-2 and SOV-1 have

concurrent spurious operation duration of three seconds, while SOV-2 and MOV-1 have

concurrent spurious operation duration of 16 seconds. Figure 4-36 provides the temperature

profile for the two cable locations that experienced concurrent hot shorts. The vertical line

represents the time of failure.

Figure 4-36. Plot of intermediate-scale test 5 for MOV and SOV cable locations

Time (s)

0 500 1000 1500 2000 2500 3000

Temperature (C)

0

200

400

600

800

B Position - Conduit - Middle

D Position - Middle

635 C

584 C

4-40

To summarize the data presented in Figure 4-36 and Table 4-35, intermediate-scale test #5

experienced two concurrent hot shorts among three circuits; the cables are physically located in

Location D and Location B (inside the conduit). All of the cable insulation is thermoplastic.

Figure 4-36 plots temperature versus time for MOV and SOV cable locations in intermediatescale test #5. According to Figure 4-36, the cables located in the B Position fail at

approximately 600 °C, whereas the cable located in the D Position fails at approximately

630 °C. This indicates the importance of understanding thermal exposure conditions and the

effect that they have on concurrent failure timing. Although the cables are in different locations,

each has a similar temperature profile, which leads to failure at approximately the same time.

Figure 4-37 depicts the DC hot short concurrence between the1-inch valve circuit and

switchgear circuits for intermediate-scale Test #6. There are two data points for the SWGR

circuits, since one is for the close function and the other for the trip function. The 1-inch valve

cable is located in position C (hot gas layer), while the switchgear close and trip cables are both

located inside a conduit at position B (lower plume). As referenced in Table 4-35, the 1-inch

valve and switchgear (close) circuits have concurrent spurious operation duration of one

second, as do the 1-inch valve and switchgear (trip) circuits.

Figure 4-37. Concurrent hot shorts - test 6

4-41

Figure 4-38. Plot of intermediate-scale test 6 for 1-inch valve and switchgear cable

locations

To summarize the data presented in Figure 4-37 and Table 4-35 intermediate-scale test #6

experienced two concurrent hot shorts among three circuits; the cables are physically located in

Locations C and B inside the conduit. All of the cable insulation is thermoplastic. Figure 4-38

plots temperature versus time for intermediate-scale test #6 for 1-inch valve and switchgear

cable locations. According to the plot, cables located in B Position fail at approximately 460 °C,

whereas the cable located in C Position fails at approximately 340 °C. Both of these

temperatures fall within the typical range of cable failures for this cable type. This plot provides

an analytical representation of the importance of cable location and the thermal exposure

conditions due to the HGL effects.

Figure 4-39 depicts the dc circuit hot short concurrence between Large Coil, SOV-1, and MOV-1

for intermediate-scale test #8. In the case of the two concurrent hot shorts observed in this test,

all circuit cables were located in Position A (flame exposure). As referenced in Table 4-35,

large coil and SOV-1 have concurrent spurious operation durations of 90 seconds, while the

large coil and MOV-1 have concurrent spurious operation durations of nine seconds. All of the

cable insulation is thermoplastic. All of the cables are located in A, in the flame; this is

consistent with the concurrent failure timing because all cables are experiencing similar thermal

insult.

Time (s)

0 500 1000 1500 2000 2500

Temperature (C)

0

100

200

300

400

500

600

C Position - Middle

B Position - Conduit Avg

412 C

343 C

4-42

Figure 4-39. Concurrent hot shorts - test 8

Figure 4-40 depicts the dc hot short concurrence as falling between SOV1 and MOV1 for

intermediate-scale test #9. In this test, all cables involved in the concurrent hot shorts were

located in the same tray, namely Position B (lower plume). As referenced in Table 4-35, SOV1

and MOV1 have concurrent spurious operation durations of seven seconds, while SOV1 and

MOV1 have concurrent spurious operation durations of one second. All of the cable insulation

is thermoset. All of the cables are located in B, in the plume; this is consistent with the

concurrent failure timing as a result of being exposed to similar thermal insults.

4-43

Figure 4-40. Concurrent hot shorts - test 9

Analysis of concurrence among all tests for a specific exposure location

As mentioned above, a comment on the draft version of this report suggested that the data

should be analyzed to evaluate the concurrence of spurious operations among all tests for

specific fire exposure locations, as was done for the AC results. For the intermediate-scale

tests, the data from all tests was binned in exposure locations A, B, and D. Locations C and E

are geometrically identical, and were grouped into one bin. Since the DC test data used the

surrogate circuits in the penlight exposure (AC data did not), that data was also analyzed and

binned by the following shroud temperature ranges: Bin 1 consisted of data from cables

exposed to 325 – 375C shroud temperatures, Bin 2 had a temperature range of 400 – 480C,

and Bin 3 had a temperature range of 500 – 525C. There was no strict rule or basis for the

selection of these bins. However, binning was chosen to make the analysis simpler, and on the

assumption that cables exposed to high heat flux (i.e., penlight shroud temperatures) should fail

earlier than cables exposed to lower heat fluxes. Additionally, binning makes the presentation

of the data cleaner and easier to understand. However, cables tend to exhibit aleatory

uncertainty with regard to their thermal fragility (i.e., cables don’t all fail at the same

temperature); thus, to provide a complete analysis of the concurrence observed during testing,

the last part of this analysis evaluates concurrences among data in these bins.

Location A in the DESIREE-FIRE tests places cables in a flame exposure location, as shown in

Figure 2-32. Location A had a total of 14 cables instrumented for circuit response during all of

the DESIREE-FIRE tests, of which eight experienced spurious operations. Of those eight test

cases, five were involved in a total of six concurrent spurious operations, and are presented in

Figure 4-41 and Table 4-36.

4-44

Figure 4-41. Time plot of concurrent spurious operations for DESIREE-FIRE among all

test circuits in Location A

Table 4-36. Test data for Location A of DESIREE-FIRE for cases where concurrent

spurious operations occurred Test ID D-IT-8-SOV1

D-IT-2-SOV2

D-IT-8-MOV1

D-IT-2-MOV2

D-IT-8-LGCOIL

of concurrent

cable SO’s

Test ID

D-IT-8-SOV1 22 - - 92 3

D-IT-2-SOV2 22 56 - 34 4

D-IT-8-MOV1 - 56 7 10 4

D-IT-2-MOV2 - - 7 - 2

D-IT-8-LGCOIL 92 34 10 - 4

Start Time (s) 960 1030 1054 1116 940

Stop Time (s) 1052 1110 1123 1139 1064

Duration (s) 92 80 69 23 124

900

950

1000

1050

1100

1150

D‐IT‐8‐SOV1 D‐IT‐2‐SOV2 D‐IT‐8‐MOV1 D‐IT‐2‐MOV2 D‐IT‐8‐LrgCl

Start

Stop

4-45

Location B in the DESIREE-FIRE tests places cables in a flame/plume exposure location

dependent on the cable loading in Location A, as shown in Figure 2-32. Location B had a total

of 38 cables instrumented for circuit response during all of the DESIREE-FIRE tests, of which

23 tests resulted in spurious operations. Of those 23 tests, 11 were involved in a total of six

concurrent spurious operations, and are presented in Table 4-37. Due to the concurrence

durations and the range of failure times among tests, a graph of these results is not presented.

Table 4-37. Test data for Location B of DESIREE-FIRE for cases where concurrent

spurious operations occurred Test ID D-IT-7-SOV1 D-IT-C2-TRP D-IT-C2-CLS D-IT-5-LGCOIL

D-IT-6-TRP

D-IT-1-1”VLV

D-IT-3-SOV2

D-IT-1-LGCOIL

D-IT-3-CLS

D-IT-9-SOV1

D-IT-9-MOV2

of concurrent

cable SO’s

Test ID

D-IT-7-SOV1 1 1 - - - - - - - - 3

D-IT-C2-TRP 1 - - - - - - - - - 2

D-IT-C2-CLS 1 - - - - - - - - - 2

D-IT-5-

LGCOIL - - - 1 - - - - - - 2

D-IT-6-TRP - - - 1 - - - - - - 2

D-IT-1-1”VLV - - - - - 30 - - - - 2

D-IT-3-SOV2 - - - - - 30 - - - - 2

D-IT-1-

LGCOIL - - - - - - - 1 - - 2

D-IT-3-CLS - - - - - - - 1 - - 2

D-IT-9-SOV1 - - - - - - - - - 10 2

D-IT-9-MOV1 - - - - - - - - - 10 2

Start Time (s) 302 334 354 819 850 1358 1361 1446 1460 2584 2613

Stop Time (s) 364 335 355 909 851 1391 1397 1465 1461 2689 2623

Duration (s) 62 1 1 90 1 33 36 19 1 105 10

The data from locations C and E was combined, due to geometric similarities with respect to the

fire exposure conditions. As such, these two locations consisted of 18 circuit trials, in which 7

spurious operations occurred. Of the seven spurious operations, none were concurrent.

Location D in the DESIREE-FIRE tests places cables in a plume exposure location, as shown in

Figure 2-32. Location D had a total of 28 cables instrumented for circuit response during all of

the DESIREE-FIRE tests, during which 16 circuits experienced spurious operations. Of these

16 spurious operations, eight were involved in a total of four concurrent spurious operations,

and are presented in Figure 4-42 and Table 4-38.

4-46

Figure 4-42. Time plot of concurrent spurious operations for DESIREE-FIRE among all

test circuits in Location D

Table 4-38. Test data for Location D of DESIREE-FIRE for cases where concurrent

spurious operations occurred Test ID D-IT-5-MOV2 D-IT-9-SOV2 D-IT-1-MOV2

D-IT-10-1”Vlv

D-IT-12-LgCoil

D-IT-3-MOV1

D-IT-11-SOV2

D-IT-3-SOV1

of concurrent

cable SO’s

Test ID

D-IT-5-MOV2 23 - - - - - - 2

D-IT-9-SOV2 23 - - - - - - 2

D-IT-1-MOV2 - - 9 - - - - 2

D-IT-10-1”Vlv - - 9 - - - - 2

D-IT-12-LgCoil - - - - 3 - - 2

D-IT-3-MOV1 - - - - 3 - - 2

D-IT-11-SOV2 - - - - - - 21 2

D-IT-3-SOV1 - - - - - - 21 2

Start Time (s) 1500 1552 2617 2635 2746 2784 2858 2860

Stop Time (s) 1575 1581 2663 2644 2798 2787 2917 2881

Duration (s) 75 29 46 9 52 3 59 21

1400

1600

1800

2000

2200

2400

2600

2800

3000

Stop

Start

4-47

For the penlight test cases exposed to shroud temperature in the range of 325 - 375C a total of

25 cables were instrumented for circuit response, 17 circuits experienced spurious operations.

Of these 17 spurious operations, Figure 4-43 and Table 4-39 present the 11 test cases that

were involved in a total of 13 concurrent spurious operations.

Figure 4-43. Time plot of concurrent spurious operations for DESIREE-FIRE among all

Penlight test with exposure temperatures in the range of 325-375C

Table 4-39. Test data for DESIREE-FIRE cases where concurrent spurious operations

occurred during Penlight exposures in the range of 325 - 375C

Test ID

D-P-9-SOV2

D-P-12-MOV1

D-P-9-SOV2

D-P-30-MOV2

D-P-11-LgCoil

D-P-11-1”Vlv

D-P-30-MOV1

D-P-JPN1-CLS

D-P-JPN3-MOV2

D-P-44-MOV1

D-P-44-MOV2

of concurrent

cable SO’s

D-P-9-SOV2 28 23 - - - - - - - - 3

D-P-12-MOV1 28 23 - - - - - - - - 3

D-P-9-SOV2 23 23 - - - - - - - - 3

D-P-30-MOV2 - - - 1052 811 91 1 193 - - 6

D-P-11-LgCoil - - - 1052 811 91 1 - - - 5

D-P-11-1”Vlv - - - 811 811 91 - - - - 4

D-P-30-MOV1 - - - 91 91 91 - - - - 4

D-P-JPN1-CLS - - - 1 1 - - - - - 3

D-P-JPN3-MOV2 - - - 193 - - - - - - 2

D-P-44-MOV1 - - - - - - - - - 225 2

D-P-44-MOV2 - - - - - - - - - 225 2

Start Time (s) 827 863 864 1076 1089 1108 1435 1977 2308 9073 10043

Stop Time (s) 891 1066 887 2503 2141 1919 1526 1978 2501 10268 10349

Duration (s) 64 203 23 1427 1052 811 91 1 193 1195 306

0

2000

4000

6000

8000

10000

12000

Stop

Start

4-48

For the penlight test cases exposed to shroud temperature in the range of 400 - 480C a total of

36 cables instrumented for circuit response, 23 circuits experienced spurious operations. Of

these 23 spurious operations, Figure 4-44 and Table 4-40 present the 15 test cases that were

involved in a total of 12 concurrent spurious operations.

Figure 4-44. Time plot of concurrent spurious operations for DESIREE-FIRE among all

Penlight test with exposure temperatures in the range of 400-480C

470

490

510

530

550

570

590

610

630

650

Stop

Start

Table 4-40. Test data for DESIREE-FIRE cases where concurrent spurious operations occurred during

Penlight exposures in the range of 400 - 480C

Test ID

D-P-8-MOV1

D-P-20-SOV1

D-P-20-SOV2

D-P-7-MOV1

D-P-2-SOV2

D-P-25-MOV2

D-P-4-TRP

D-P-22-MOV1

D-P-22-MOV2

D-P-6-1”Vlv

D-P-25-MOV1

D-P-5-LgCoil

D-P-4-CLS

of concurrent

cable SOs Test ID

D-P-8-MOV1 9 3 - - - - - - - - - - - - 3

D-P-20-SOV1 9 17 4 - - - - - - - - - - - 4

D-P-20-SOV2 3 17 34 13 - - - - - - - - - - 5

D-P-7-MOV1 - 4 34 15 - - - - - - - - - - 4

D-P-1-SOV2 - - 13 15 20 - - - - - - - - - 4

D-P-2-SOV2 - - - - 20

3

5

3

3 - - - - - 6

D-P-25-MOV2 - - - - - 3 - - - - - - - - 2

D-P-25-MOV2 - - - - - 5 - 3

3 - - - - - 4

D-P-4-TRP - - - - - 3 - 3

4 1 - - - - 5

D-P-22-MOV1 - - - - - 3 - 3

4 33 1 9

3 - 8

D-P-22-MOV2 - - - - - - - - 1 33 1 11

3 1 7

D-P-6-1”Vlv - - - - - - - - - 1 1 - - - 3

D-P-25-MOV1 - - - - - - - - - 9 11 - 3 - 4

D-P-5-LrgCoil - - - - - - - - - 3

3 - 3 - 4

D-P-4-CLS - - - - - - - - - - 1 - - - 2

Start Time (s) 501 502 508 521 542 559 580 584 586 586 589 598 613 616 625

Stop Time (s) 511 525 555 557 579 589 583 589 590 622 631 599 624 619 626

Duration (s) 10 23 47 36 37 30

3

5

4 36 42 1 11

3 1

4-49

4-50

For the penlight test cases exposed to shroud temperature in the range of 500 - 525C a total of

12 cables instrumented for circuit response, nine circuits experienced spurious operations. Of

these nine spurious operations, Figure 4-45 and Table 4-41 present the six test cases that were

involved in a total of three concurrent spurious operations.

Figure 4-45. Time plot of concurrent spurious operations for DESIREE-FIRE among all

Penlight test with exposure temperatures in the range of 500-525C

Table 4-41. Test data for DESIREE-FIRE cases where concurrent spurious operations

occurred during Penlight exposures in the range of 500 - 525C Test ID D-P-37-MOV1 D-P-35-CLS D-P-37-MOV2 D-P-34-SOV1 D-P-41-MOV2 D-P-41-MOV1 # of concurrent cable SO’s

Test ID

D-P-37-MOV1 1 - - - - 2

D-P-35-CLS 1 - - - - 2

D-P-37-MOV2 - - 12 - - 2

D-P-34-SOV1 - - 12 - - 2

D-P-41-MOV2 - - - - 54 2

D-P-41-MOV1 - - - - 54 2

Start Time (s) 1681 1693 1724 1728 2463 2702

Stop Time (s) 1712 1694 1740 1743 2894 2756

Duration (s) 31 1 16 15 431 54

The above information completes the evaluation of penlight data for individual bins, however,

since there was no strict rule for developing these bins, among other reasons stated previously,

1600

1800

2000

2200

2400

2600

2800

3000

Start

Stop

4-51

the following and final concurrence analysis evaluates concurrent spurious operations occurring

between test cases in different bins. Of the 73 penlight tests, 51 spurious operations occurred.

Out of the 51 spurious operations, there were 76 instances of concurrent spurious operations

and of those 76 concurrences, 34 instances of concurrent spurious operation occurred between

test cases in different bins. Thus, the binning provided a method to easily present the data, but

the basis for selecting the bins is weak. Table 4-42 presents the cases where spurious

operation concurrence was identified between test cases in different bins. The “*” symbol is

used in the table to indicate spurious operation concurrence for test cases in the same bin, thus,

the table below does not represent duplicate concurrences previously presented.

Conclusions

Upon reviewing the test data for AC and DC circuits with respect to the observation of

concurrence, several insights have been gained. First the lack of concurrence within any

individual AC intermediate-scale test provides no bases for excluding plausibility of this

phenomena. The experimental arrangement of cables within the test apparatus somewhat

biased the results to decrease the possibility of observing concurrent spurious operations. This

was because of the limited number of cables instrumented for circuit response (four SCDUs)

and the placement of cables in different locations or in the same locations but with different

bundling configurations caused the cables to receive different thermal exposures. What would

be more commonly found in NPP applications would be cable raceways loaded with cables of

the same insulation type (TS, TP) and exposures to the same thermal insult. With this

arrangement groups of cables within the same cable tray would be exposed to almost identical

thermal conditions and with similar cable failure thresholds it is likely that concurrent spurious

operations would be observed.

The DC results provided a better understanding of the concurrent spurious operation

phenomena. Here up to eight cables could be instrumented for circuit response per test and of

the five exposure locations within the testing apparatus, typically only two locations were used.

This resulted in multiple cables in the same location being exposed to similar thermal

conditions. The flame (location A) concurrence in the intermediate-scale DC tests reflect the

data obtained from the DC Penlight experiments showing the likelihood of concurrent spurious

operations to be in the range of 36-52%. For the DC intermediate-scale locations other than

location A (flame) the results showed a lower likelihood of concurrence, in the range of 29%.

This result is difficult to explain, but is likely linked to the likelihood of individual spurious

operation results presented previously in section 2 and 4 when evaluation the parameter effect

of thermal exposure conditions where it was shown that the likelihood of spurious operation for

the flame and radiant exposures were higher than the plume or hot gas layer results.

The final insight gained from this review of the data was that the duration of spurious operations

can influence the likelihood of concurrent spurious operations. This finding is easily understood

and Table 4-42 shows instances where long duration spurious operations resulted in numerous

concurrent spurious operations (e.g., D-P-MOV2, D-P-11-LgCoil, D-P-11-1”Vlv).

Table 4-42. Test data for DESIREE-FIRE cases where concurrent spurious operations occurred during

Penlight exposures among tests not binned together in the analysis presented previously.

indicates a concurrent spurious operation that was between tests within the same bin and captured in the bin analysis above.

Test ID

D-P-20-SOV1

D-P-20-SOV2

D-P-31-SOV1

D-P-1-SOV2

D-P-2-SOV2

D-P-33-MOV2

D-P-22-MOV1

D-P-22-MOV2

D-P-32-Cls

D-P-25-MOV1

D-P-32-Trp

D-P-12-MOV1

D-P-21-Cls

D-P-30-MOV2

D-P-11-lrgCl

D-P-11-1"Vlv

D-P-50-MOV2

D-P-41-MOV2

D-P-30-MOV1

D-P-36-1"Vlv

D-P-37-MOV1

D-P-35-Cls

D-P-37-MOV2

D-P-34-SOV1

D-P-JPN3-MOV2

D-P-41-MOV2

D-P-JPN3-MOV1

D-P-41-MOV1

D-P-20-SOV1 * 3 ‐‐‐‐‐‐‐‐ ‐ ‐ ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

D-P-20-SOV2 * 3 * ‐‐‐‐‐‐‐ ‐ ‐ ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

D-P-31-SOV1 3 3 ‐‐‐‐‐‐‐‐ ‐ ‐ ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

D-P-1-SOV2 ‐ * ‐ * 1 ‐‐‐‐‐ ‐ ‐ ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

D-P-2-SOV2 ‐‐‐ * 1 * ‐‐‐‐ ‐ ‐ ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

D-P-33-MOV2 ‐‐‐ 1 1 ‐‐‐‐‐ ‐ ‐ ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

D-P-22-MOV1 ‐‐‐‐ * ‐ * 1 * 1 ‐‐‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐

D-P-22-MOV2 ‐‐‐‐‐‐ * 1 * 1 ‐‐‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐

D-P-32-Cls ‐‐‐‐‐‐ 1 1 ‐‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐

D-P-25-MOV1 ‐‐‐‐‐‐ * * ‐ 1 ‐‐‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐

D-P-32-Trp ‐‐‐‐‐‐ 1 1 ‐ 1 ‐‐‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐

D-P-12-MOV1 ‐‐‐‐‐‐‐‐‐‐‐ 1 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

D-P-21-Cls ‐‐‐‐‐‐‐‐‐‐‐ 1 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

D-P-30-MOV2 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ * * 24 99 * 13 31 1 16 15 * * ‐ ‐

D-P-11-lrgCl ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ * * 24 99 * 13 31 1 16 15 ‐‐‐‐

D-P-11-1"Vlv ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ * * 24 99 * 13 31 1 16 15 ‐‐‐‐

D-P-50-MOV2 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ 24 24 24 ‐‐‐‐‐‐‐‐‐‐‐

D-P-41-MOV2 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ 99 99 99 ‐ ‐‐‐‐‐‐‐‐‐‐

D-P-30-MOV1 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ *** ‐‐ ‐‐‐‐‐‐‐‐‐

D-P-36-1"Vlv ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ 13 13 13 ‐‐‐ ‐‐‐‐‐‐‐‐

D-P-37-MOV1 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ 31 31 31 ‐‐‐‐ * ‐‐‐‐‐‐

D-P-35-Cls ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ 111 ‐‐‐‐ * ‐‐‐‐‐‐

D-P-37-MOV2 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ 16 16 16 ‐‐‐‐‐‐ * ‐‐‐‐

D-P-34-SOV1 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ 15 15 15 ‐‐‐‐‐‐ * ‐‐‐‐

D-P-JPN3-MOV2 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ * ‐‐‐‐‐‐‐‐‐‐ 38 ‐ ‐

D-P-41-MOV2 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ * ‐‐‐‐‐‐‐‐‐‐ 38 235 *

D-P-JPN3-MOV1 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ ‐‐‐‐‐‐‐‐‐‐‐‐ 235 54

D-P-41-MOV1 ‐‐‐‐‐‐‐‐‐‐‐ ‐ ‐ ‐‐‐‐‐‐‐‐‐‐‐‐‐ 54

Start 502 508 518 542 559 574 586 589 607 613 620 863 962 1076 1089 1108 1241 1307 1435 1611 1681 1693 1724 1728 2308 2463 2632 2702

Stop 525 555 521 579 589 575 622 631 608 624 621 1066 963 2503 2141 1919 1265 1406 1526 1624 1712 1694 1740 1743 2501 2894 2867 2756

Duration 23 47 3 37 30 1 36 42 1 11 1 203 1 1427 1052 811 24 99 91 13 31 1 16 15 193 431 235 54

4-52

5-1

5. INTER-CABLE – DIRECT CURRENT CIRCUITS

5.1 Traditional Inter-Cable Failure Analysis for DESIREE-FIRE

Results

As was done in other testing projects, the Direct Current Electrical Shorting in Response to

Exposure Fire (DESIREE-FIRE) project attempted to evaluate inter-cable interactions using

multiple methods. To explicitly explore this failure mode, an inter-cable test configuration was

used. In addition, the data (voltage and current measurements) from the surrogate circuits

could be analyzed post-test to evaluate inter-cable shorting behavior.

The inter-cable test configuration used during the DESIREE-FIRE testing focused on arranging

the cables to evaluate the likelihood of proper polarity in inter-cable shorting. These tests

stacked the deck by placing the cables on an insulated marinite board located in a cable tray

and having multiple source cables surrounding a single target cable. This configuration is

shown in Figure 5-1, with a target cable co-located in the center of the arrangement and two

positive source cables and two negative source cables located on the side and above a target

cable. The target cable conductors were all connected to a network of resistors and monitored

for voltage response only (no current transducers were used). Each source conductor was

powered by one side of a nominal 125Vdc battery and protected with a 10-amp fuse.

Figure 5-1. DESIREE-FIRE inter-cable configuration

Thirteen intermediate-scale and four penlight tests were conducted using the five-cable intercable arrangement shown above. Of those tests, only one showed weak signs of multiple

external shorts to separate conductors within the target cable. This particular case is shown in

Figure 5-2, where the maximum induced voltage difference is roughly 20Vdc. In all other tests,

the data shows that internal faults occurred prior to inter-cable faulting of the target cable.

5-2

Figure 5-2. DESIREE-FIRE inter-cable test results penlight test 47

The second method involved reviewing the voltage and current data from individual tests. Intercable short circuit failures involve conductors of separate cables coming in electrical contact

with each other due to fire damage. When analyzing the data for these types of failures, voltage

and current traces are needed to understand which conductors are involved (i.e., voltage alone

will not provide sufficient information to identify source and target conductors). In addition,

knowledge of fuse operability is beneficial so that potential sources can be ruled out following

the clearing of these protective devices. The DC test circuits all had two fuses, one on the

positive battery side and one on the negative battery side of the circuit. When a circuit’s positive

battery side fuse cleared, it could no longer be considered a potential source; likewise, when its

negative fuse cleared, its target conductors could no longer be considered targets (i.e., hot

shorts to active and passive devices could no longer occur). However, if only one of the two

circuit fuses cleared, then the circuit could still experience inter-cable shorting faults that could

cause spurious operations.

The small-scale penlight tests were simpler to evaluate for inter-cable shorting because there

were typically no more than two circuits in any individual test. The intermediate-scale testing,

however, used all seven circuits (eight energized cables), along with the inter-cable testing

configuration. The larger number of circuits provided additional source and target conductor

shorting opportunities, and complicated the evaluation of the inter-cable shorting events.

The ungrounded battery supply also provided complications in analyzing the data for inter-cable

shorting. If the dc battery is ungrounded, which is common practice in U.S. nuclear power

plants (NPPs), a single short to ground from a positively or negatively energized conductor

would not cause a fuse to clear in and of itself. To have a fuse clear either a plus or a minus, a

conductor-to-conductor short would be required, or multiple shorts to a ground plane (plus and

minus) of sufficiently low resistance to result in over current, either of which would clear a circuit

Time (seconds)

2000 3000 4000 5000 6000 7000 8000

Voltage (Vdc)

40

50

60

70

80

T1-V(Batt-)

T2-V(Batt-)

T3-V(Batt-)

T4-V(Batt-)

T5-V(Batt-)

T6-V(Batt-)

T7-V(Batt-)

T5

T2

5-3

protective device. However, because the dc circuit had two fuses per circuit, one on the positive

side and one on the negative side, the fuses would not always clear simultaneously. Thus, in

about half of the cases, only one fuse in a particular circuit would clear at any time. This singlefuse clearing would eliminate the possibility of intra-cable shorting, but the side of the circuit

whose fuse did not clear would still be functional from an inter-cable shorting perspective. For

example, if circuit A experienced a low-resistance short when its positive side fuse cleared, but

its negative fuse remained intact, then this circuit could still experience a short from another

conductor in another cable, which could lead to a spurious operation if the respective

conductors shorted together.

The purpose of this lengthy discussion is to identify a unique failure mode that has not been

observed thus far in the associated testing. With a common ungrounded power supply, the

ground plane (cable trays, conduit, and ground conductors) can act as an electrical conductive

pathway to aid in inter-cable shorting. This observation results in the need to analyze hot shorts

and spurious operations more closely to identify the failure mode type (inter- or intra-cable). In

the AC tests, the control power transformer (CPT) was typically grounded (as is done in the

majority of U.S. NPPs), and any energized conductor experiencing a low-resistance short to the

reference ground (due to fire damage) would experience a high-current rush, resulting in the

clearing of an upstream protective device (fuse or circuit breaker) and the de-energizing of the

circuit.

To aid in identifying inter-cable shorting, a simple yet beneficial approach was taken. For an

individual circuit (MOV-1, SOV-2, Lg Coil, etc.), the current within that circuit was summed, that

is, the currents coming from the positive battery terminal were added and the currents returning

to the negative battery terminal were subtracted. Figure 5-3 and Equation 5-1 provide the

graphical and mathematical representations of this approach. Under normal conditions,

Kirchoff’s current law states that the currents within a circuit sum up to zero. This law also holds

under intra-cable-only circuit failures, in that the current within the circuit/cable remains inside

the cable, and the sum is equal to zero. However, when inter-cable interactions occur, the

current from one circuit leaves the electrical circuit and enters another; thus, for the inter-cable

case, the individual circuit currents do not sum up to zero, and there is a net current (negative if

the circuit is receiving currents from some other circuit, positive if the circuit is supplying

currents to some other circuit).

5-4

Figure 5-3. DC MOV schematic showing current summation used in identifying intercable shorting behavior

isum_dcMOV = iP + iG + iR - ( iYC1 + iYO1 + iN ) Equation 5-1

Although this method provides an efficient tool to quickly identify which circuits were involved in

inter-cable shorting, there are a few drawbacks. First, this method only shows which circuits

were involved, and not which conductors. To compensate for this, the analyst must review the

data from the respective circuits and determine which conductors were involved. Secondly, in

the intermediate-scale testing, the inter-cable circuit was included, but it was not monitored for

current. Thus, in some cases the analysis could not identify the source of the inter-cable short,

although it can be assumed that the source was the inter-cable circuit. Thirdly, there were a few

circuits (small SOVs in particular) that had a very low operating current (0.042A) when

energized. Although they were typically discernible in the analysis, they were not as apparent

as the other circuits’ inter-cable shorts. Fourthly, there may be cases where a circuit is leaking

current and gaining current from other circuits simultaneously; these interactions can cancel

each other out, and can lead to difficulties in identifying the inter-cable short. Lastly, there were

several cases where a single circuit shorted abruptly to the common ground plane and caused

several circuit protective devices to clear without direct indication of which circuit initiated the

event. It is assumed that because there were multiple simultaneous fuse clears, there was a

very abrupt current spike, followed by fuse clearing, which the data acquisition system (DAQ)

was unable to capture.

As a result of these aspects, the analysis for this section is focused on identifying spurious

operations that resulted from inter-cable (cable-to-cable) shorting. There were some cases

where it was possible to determine how individual circuit fuses cleared via inter-cable shorting;

that information is noted in the summary tables. At this time, an evaluation of inter-cable hot

shorting of the passive targets has not been conducted, mainly due to the low-level currents

required to energize these devices and the complications associated with the auxiliary contacts

and reed switches used to control the passive target sources.

5-5

The following two sections present the inter-cable analysis of the surrogate circuit data for the

small-scale Penlight and intermediate-scale open-flame tests. Due to the number of circuits

used in the intermediate-scale testing and the use of actual flaming combustions, those results

are analyzed in more detail than they are in the penlight tests, where only two circuits were colocated within the same cable tray. The intermediate-scale results also show unique failures in

which cables located within a rigid steel conduit interact with other cables located in cable trays

at different locations.

5.2 Penlight Tests – Ground Fault Equivalent Hot Short

Penlight tests for the DESIREE-FIRE project typically consisted of two cables, each connected

to an individual circuit. The only exception for this type of configuration was the medium-voltage

circuit breaker test, where two cables were connected to one circuit. In all tests using a cable

tray, the cables were not in physical contact with anything except the cable tray. A cable

instrumented for thermal response was typically placed between the two cables instrumented

for electrical response, as shown in Figure 5-4. Thus, any inter-cable interactions are a direct

result of cable interactions with the cable tray. In conduit tests, the two electrically monitored

cables may be in physical contact, and a more detailed evaluation of any inter-cable interactions

is necessary.

Figure 5-4. Penlight cable tray typical loading, showing two electrically instrumented

cables and a thermal response (temperature recording) cable located in the

center.

The Penlight results of the ground equivalent hot shorting analysis are documented in Appendix

A. A summary of this analysis is presented here in Table 5-1.

5-6

Table 5-1. Results of inter-cable shorting during Penlight DESIREE-Fire tests.

Test # Failure Mode Description

PT-8 MOV-2 hot short to “R” conductor from MOV-1 “P” conductor at 478 seconds

(duration = 3 seconds).

PT-12 Interactions between MOV-1 “N” conductor and MOV-2 “P” conductor. This is a

case of a high-resistance short between conductors connected to positive and

negative battery potential.

PT-22 Four separate ground fault equivalent spurious operations occurred in this test.

MOV-1 Open coil SO for 2 seconds, short from MOV-2 “G” conductor (starts at 585s)

MOV-1 Open coil SO for 2 seconds, short from MOV-2 “G” conductor (starts at 589s)

MOV-1 Open coil SO for 40 seconds, short from MOV-2 “G” conductor (starts at

593s)

MOV-2 Open coil SO for 38 seconds, short from MOV-1 “G” conductor (starts at

595s)

PT-33 Interactions between MOV-1 “P” conductor and MOV-2 “N” and “YC” conductors (No

SO or HS occur).

PT-37 MOV-2 Close coil SO for 16 seconds, short from MOV-1 “G” conductor to MOV-2

“YC” conductor.

PT-41 Two separate ground fault equivalent spurious operations occurred in this test.

MOV-2 Close coil SO for 6 seconds, short from MOV-1 “G” conductor to MOV-2 “YC”

conductor (starts at 2753s)

MOV-1 Open coil SO for 1 second, short from MOV-2 “G” conductor to MOV-1 “YO”

Interactions between MOV-1 “P” conductor and MOV-2 “N” conductor were also

observed for approximately 9 seconds, starting at 2825 seconds.

PT-49 MOV-2 Open coil SO for <1 second, source is difficult to identify due to other

conductor interactions among cable trays.

PT-50 MOV-2 Close coil SO for 22s, short from MOV-1 “G” conductor to MOV-2 “YC”

conductor.

Inter-cable interactions also cause a fuse clear on MOV-2 circuit.

PT-JPN3 False indication on MOV-1 Red lamp ON, due to inter-cable shorting with MOV-2.

PT-20 SOV-2 SO for 20 seconds, short from SOV-1 “G” conductor (starts at 508s).

PT-28 SOV-2 SO for 297secodns, short from SOV-1 “P” conductor (starts at 3393s).

PT-31 False indication on SOV-2 Green lamp ON, due to inter-cable shorting with SOV-1.

PT-11 Two separate ground equivalent hot shorts were observed in this test.

Large coil SO for 52 seconds, short from 1-inch valve “G” and “R” conductors

1-inch valve SO for 798 seconds, short from large coil “P” conductor

PT-40 Large coil SO for 64 seconds, short from 1-inch valve “G” and R” conductors (starts

at 4100s).

PT-4 SWGR-trip SO (breaker opens), short from SWGR-Close “N1” conductor.

PT-JPN2 False indication Red lamp ON, inter-cable interaction between SWGR-Trip “R”

conductor and SWGR-Close “N1” conductor.

5.3 Intermediate-Scale Tests – Ground Fault Equivalent Hot Short

5.3.1 Preliminary Test #1

Figure 5-5 presents an illustration of the test set-up for preliminary test #1. Location A contains

fill cable that is represented by the gray area located within the cable tray, and is located directly

5-7

above the fire source (200 kW propene diffusion sand burner). Location B contains two cables

connected to the switchgear trip and close coil circuitry, location C contains two cables

connected to two separate AC surrogate circuit diagnostic units (SCDUs), location D contains

the inter-cable test configuration of cables, and location E contains two cables connected to the

1-inch valve and the large coil. During testing, the openings in the hood in which the cable trays

and conduits are located are enclosed with a ceramic fiber material to develop and maintain a

hot gas layer that is sufficient to damage the cables. The illustration does not show ceramic

fiber.

Figure 5-5. Intermediate-scale test preliminary 1 cable loading configuration

Table 5-2 presents the failure mode sequence of events of preliminary test #1. The AC SCDU

and inter-cable testing results are not discussed. Cables in location E did not fail during the

test.

Table 5-2. Intermediate-scale preliminary test 1

Time (s) Failure Observation

502 SWGR-C SA

504 SWGR-C Fuse Clear – Positive

515 SWGR-T Fuse Clear – Negative

540 SWGR-C Fuse Clear – Negative (INTER-CABLE with SWGR-T cond. ‘P’)

NOTE: 1-inch valve and Lg Coil circuit did not fail max temp (~380 C for both

TS cables)

5.3.2 Preliminary Test #2

Figure 5-6 and Table 5-3 provide an illustration of the intermediate-scale layout and a summary

of the test circuit failure sequence, respectively. Bold font is used to identify inter-cable

interactions. Figure 5-7 presents the summed current plots for all circuits in this test. This plot

indicates that MOV-2 open coil experiences an inter-cable hot short-induced spurious operation

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

ac1-4 : SCDU circuits

+/- : power source cable 35A

NOT TO SCALE

Inter-cable Circuit

SG-C SG-T

ac3 ac4 1V LC

5-8

from SOV-2. Although the cables associated with MOV-2 and SOV-2 are in the same cable

tray, they are not in physical contact with each other; thus, the only means for this interaction is

by ground plane equivalent hot short failure mode. In this specific spurious operation,

conductors “S1,” “P,” and “G” of the SOV-2 circuit are supplying power to the MOV-2 open coil

contact conductor.

Figure 5-6. Intermediate-scale test preliminary 2 cable loading configuration

Table 5-3. Intermediate-scale preliminary test 2

Time (s) Failure Observation

312 SOV-1 Fuse Clear – Positive

343 MOV-1 Fuse Clear – Positive & Negative

820 – 1221 MOV-2 SO Open Coil

INTER-CABLE shorting with SOV-2 conductor S1, P, G

888 – 1221 MOV-2 HS Close Coil (likely from inter-cable)

953 – 1020 SOV-2 SO (voltage but no corresponding current – unlikely an SO per SNL

report)

1020 SOV-2 Fuse Clear – Negative

1221 MOV-2 Fuse Clear – Negative

1221 SOV-2 Fuse Clear – Positive

5-9

Figure 5-7. Intermediate-scale test preliminary 2 – inter-cable shorting between SOV-2

and MOV-2

5.3.3 Test 1

Figure 5-8 and Table 5-4 present an illustration of the intermediate-scale cable layout and the

circuit response summary information, with inter-cable interactions shown in boldface type.

Figure 5-9 provides an indication that the 1-inch valve circuit experienced interactions with the

large coil and MOV-1 circuits. Upon closer review of the test data, it was determined that

conductor “P” of the 1-inch valve circuit energized the conductor “S” of the large coil circuit,

causing an inter-cable spurious operation. Shortly after the large coil spurious operation

cleared, MOV-1 conductor YO1 on the open coil was energized by the same “P” conductor of

the 1-inch valve circuit, causing spurious operation on the MOV-1 circuit. The 1-inch valve

source conductor “P” energized two individual conductors in different cables and separate

raceways. In addition, review of the ground fault circuitry measurements indicates that the

positive side of the battery was grounded during these interactions. These results provide a

clear indication that the ground plane was involved during both inter-cable hot shorts.

Time (s)

800 900 1000 1100 1200 1300

Current (A)

-0.20

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

0.20

1-inch Valve

Large Coil

MOV-1

MOV-2

SOV-1

SOV-2

Switchgear

5-10

Figure 5-8. Intermediate-scale test 1 cable loading configuration

Table 5-4. Intermediate-scale test 1

Time (s) Failure Observation

1361-1377 1-inch Valve SA

1375 SOV-1 Fuse Clear – Negative

1382 – 1384 1-inch Valve SA

1396 1-inch Fuse Clear – Negative

1449 Lg Coil SA

INTER-CABLE from 1-inch valve conductor P via Ground

1452 Lg Coil SA

INTER-CABLE from 1-inch valve conductor P via Ground

1460 – 1463 Lg Coil SA

INTER-CABLE from 1-inch valve conductor P via Ground

1467 Lg Coil Fuse Clear – Negative

1475 – 1558 MOV-1 SO Open Coil

INTER-CABLE from 1-inch valve conductors P and G via Ground

1516 – 1558 MOV-1 HS Close Coil

1558 MOV-1 Fuse Clear – Negative

1560 1-inch Valve Fuse Clear – Positive

2196 SWGR-C Fuse Clear – Negative

2269 MOV-1 Fuse Clear – Positive

2295 SOV-1 Fuse Clear – Positive

2512-2523 SOV-2 SA

2617 – 2661 MOV-2 HS Close Coil

2649 SOV-2 Fuse Clear – Positive & Negative

2654 – 2661 MOV-2 SO Open Coil

2663 MOV-2 Fuse Clear – Positive & Negative

2934 Lg Coil Fuse Clear – Positive

3938 – 4028 SWGR-T HS

5-11

Figure 5-9. Outstanding current hot shorting for intermediate-scale test 1 between 1-inch

valve, large coil, and MOV-1 circuits

5.3.4 Test 2

Table 5-5 presents the circuit failure chronologically. No inter-cable hot shorts occurred during

this test. However, the cause of the fuse clear on SOV-2 is a result of inter-cable shorting

between the SOV-2 and MOV-2 cables. These two cables were located in the same cable tray

in the middle of the tray cable fill (see Figure 5-10). Review of the ground fault circuit data

indicates that the battery negative was shorted to ground prior to the SOV-2 fuse clear. Thus, it

is likely that the “N” conductor in SOV-2 shorted to ground initially, followed by MOV-2’s “P”

conductor shorting to ground, resulting in an increased current, which would have caused the

fuse in SOV-2 to clear. The current summation plot showing these interactions is presented in

Figure 5-11.

Time (s)

1350 1400 1450 1500 1550 1600

Current (A)

-4

-2

0

2

4

1-inch Valve

Large Coil

MOV-1

MOV-2

SOV-1

SOV-2

Switchgear

5-12

Figure 5-10. Intermediate-scale test 2 cable loading

Table 5-5. Intermediate-scale test 2

Time (s) Failure Observation

1030-1109 SOV-2 SA

1116 - 1142 MOV-2 HS Close

1145 - 1152 MOV-2 HS Close

1145 - 1152 MOV-2 HS Open

1156 - 1175 MOV-2 HS Close

1156 - 1173 MOV-2 HS Open

1164 SOV-2 Fuse Clear – Positive and Negative

Due to INTER-CABLE shorting with MOV-2 conductor P via Gnd

3909-3977 SOV-1 SA

3979 SOV-1 Fuse Clear – Negative

3975 1-inch Valve Fuse Clear – Positive

4247 - 4362 MOV-1 SO Open

4492 Lg Coil Fuse Clear - Negative

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

IC : Inter-cable circuit

M2 S2

M1 S1

1V LC

NOT TO SCALE

Inter-cable Circuit

5-13

Figure 5-11. Outstanding current shorting in intermediate-scale test 2, between SOV-2

and MOV-2

5.3.5 Test 3

Three circuits were involved in inter-cable hot shorting during Intermediate-Scale Test #3.

Figure 5-12 illustrates the cable loading arrangement, and Table 5-6 provides a circuit fault

summary for Intermediate-Scale test 3. SOV-2 experienced two spurious operations as a result

of an inter-cable hot short from the Switchgear Trip circuit cable located in a conduit. Because

the switchgear cables were isolated from the other cables by their location in a conduit, the only

possible way for this shorting to occur was through the ground plane. Figure 5-13 provides the

current sum method plot showing the SOV-2 and switchgear circuit interactions.

Following the SOV-2 spurious operations, the 1-inch valve circuit also experienced two spurious

operations. Upon review of the voltage and current data, both 1-inch valve spurious operations

were also caused by inter-cable shorting through the ground plane from the switchgear trip

circuit. Figure 5-14 provides the current sum method plot showing the 1-inch valve and

switchgear interaction.

Time (s)

1100 1120 1140 1160 1180 1200

Current (A)

-5

0

5

10

1-inch Valve

Large Coil

MOV-1

MOV-2

SOV-1

SOV-2

Switchgear

5-14

Figure 5-12. Intermediate-scale test 3 cable loading

Table 5-6. Intermediate-scale test 3

Time (s) Failure Observation

1078 – 1090 MOV-2 SO Open Coil

1097 – 1128 MOV-2 SO Open Coil

1108 MOV-2 HS Close Coil

1111 – 1113 MOV-2 HS Close Coil

1127 MOV-2 HS Close Coil

1130 MOV-2 Fuse Clear – Positive

1168 MOV-2 Fuse Clear – Negative

1262 SOV-2 Fuse Clear – Positive

1361 – 1363 SOV-2 SO

INTER-CABLE from SWGR-T conductor P via Ground

1375 – 1406 SOV-2 SO

INTER-CABLE from SWGR-T conductor P via Ground

1419 SOV-2 Fuse Clear – Negative

1460 – 1468 SWGR-C SO

1468 SWGR-C Fuse Clear Positive and Negative

2188 – 2221 1-inch Valve SO

INTER-CABLE from SWGR-T conductor P via Ground

2226 – 2229 1-inch Valve SO

INTER-CABLE from SWGR-T conductor P via Ground

2231 1-inch Valve Fuse Clear – Negative

2286 1-inch Valve Fuse Clear – Positive

2288 Lg Coil Fuse Clear – Positive & Negative

INTER-CABLE SWGR-T conductor PT

2784 – 2787 MOV-1 SO Open Coil

2787 MOV-1 SO Fuse Clear – Positive and Negative

3066 SOV-1 Fuse Clear – Positive and Negative

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

M2 S2 SG-C

M1 S1

SG-T

1V LC

NOT TO SCALE Inter-cable Circuit

5-15

Figure 5-13. Outstanding current shorting in intermediate-scale test 3, between SOV-2

and SWGR-T

Figure 5-14. Outstanding current shorting in intermediate-scale test 3, between 1 inch

valve and SWGR-T

Time (s)

1340 1360 1380 1400 1420

Current (A)

-4

-2

0

2

4

1-inch Valve

Large Coil

MOV-1

MOV-2

SOV-1

SOV-2

Switchgear

Time (s)

2140 2160 2180 2200 2220 2240

Current (A)

-1.0

-0.5

0.0

0.5

1.0

1-inch Valve

Large Coil

MOV-1

MOV-2

SOV-1

SOV-2

Switchgear

5-16

5.3.6 Test 4

No inter-cable spurious operations were observed during this test. Figure 5-15 provides a cable

loading illustration, and Table 5-7 provides the chronology of circuit failures. The fuse clearing

for the 1-inch valve circuit and the large coil circuit were caused by inter-cable shorting from the

inter-cable circuit.

Figure 5-15. Intermediate-scale test 4 cable loading

Table 5-7. Intermediate-scale test 4

Time (s) Failure Observation

1530 1-inch valve Fuse Clear – Positive

1585 SOV-1 Fuse Clear – Positive – inter-cable with 1-inch valve conductor N

1671 Lg coil Fuse Clear – Positive

INTER-CABLE shorting from 1-inch valve conductor “N”

1671 1-inch valve Fuse Clear – Negative

INTER-CABLE shorting from Lg coil conductor “G”

1859 – 1895 MOV-1 SO Open Coil

1895 MOV-1 Fuse Clear – Positive and Negative

4766 SWGR-C Fuse Clear – Positive and Negative

4974 MOV-2 Fuse Clear – Positive and Negative

5216 – 5249 SOV-2 SO

5249 SOV-2 Fuse Clear – Positive and Negative

5305 SOV-1 Fuse Clear – Negative

5307 Lg coil Fuse Clear – Negative

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

IC : Inter-cable circuit

ac1-4 : SCDU circuits

ac1 ac2

ac3 ac4

NOT TO SCALE

Inter-cable Circuit

LC M1 S1 1V

M2 S2 SG-C SG-T

5-17

5.3.7 Test 5

Figure 5-16 provides intermediate-scale test 5 cable loading, while Table 5-8 presents the circuit

failure mode information in chronological order. As shown in Figure 5-17, SOV-1 experienced

an inter-cable hot short at 1637 seconds from the SWGRSWGR-T circuit, which resulted in a

spurious operation of the SOV-1 circuit. Conductor “PT” of the switchgear trip circuit shorted to

ground, as did the SOV-1 coil conductor “S.” These two cables were located in different areas

of the enclosure, and SOV-1 was actually located in a rigid steel conduit. Thus, these

interactions required the ground plan. No other inter-cable spurious operations were identified.

Figure 5-16. Intermediate-scale test 5 cable loading

Table 5-8. Intermediate-scale test 5

Time (s) Failure Observation

655 1-inch valve Fuse Clear – Negative

819 – 908 Lg Coil SA

908 1-inch Valve Fuse Clear – Positive

910 Lg Coil Fuse Clear – Negative and Positive

1424-1429 SWGR-C SO Close

1429 SWGR-C Fuse Clear – Positive

1500 – 1573 MOV-2 Hot Short Close Coil

1510 – 1532 MOV-2 Hot Short Open Coil

1542 – 1573 MOV-2 Hot Short Open Coil

1556 SOV-1 Fuse Clear – Positive

1575 MOV-2 Fuse Clear – Positive and Negative

1596 SWGR-C Fuse Clear – Negative

1637 – 1649 SOV-1 SA

INTER-CABLE shorting from SWGR-T conductor PT

1646 – 1658 SOV-2 SA

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

IC : Inter-cable circuit

ac1-4 : SCDU circuits

1V LC S1

M2 S2

M1

SG-C SG-T

NOT TO SCALE

Inter-cable Circuit

5-18

Table 5-8. Intermediate-scale test 5

Time (s) Failure Observation

1651 SOV-1 Fuse Clear – Negative

1667 – 1857 SOV-2 SA

1859 SOV-2 Fuse Clear – Negative

2255 SOV-2 Fuse Clear – Positive

1717 – 1734 MOV-1 SO Open Coil

1717 – 1734 MOV-1 HS Close Coil

1734 MOV-1 Fuse Clear – Positive and Negative

Figure 5-17. Outstanding current shorting in intermediate-scale test 5, between SOV-1

and SWGR-T

5.3.8 Test 6

No inter-cable hot shorts resulted in spurious operation of any device in intermediate-scale

test 6. Figure 5-18 illustrates the cable loading and arrangement for intermediate-scale test 6.

Table 5-9 presents the summary of circuit failure modes in chronological order. There were

several inter-cable interactions observed in the data set involving the MOV-2 circuit fuses

clearing as a result of inter-cable shorting with the SOV-2 and SWGR-T circuits. There were

also several current spikes in several circuit data plots, which were a result of inter-cable

shorting. Although MOV-2 and SOV-2 were collocated in the same raceway, the switchgear

circuit was in a different location, and shorting via the ground plane was likely the cause of

these interactions.

Time (s)

1500 1550 1600 1650 1700

Current (A)

-0.1

0.0

0.1

0.2

1-inch Valve

Large Coil

5-19

Figure 5-18. Intermediate-scale test 6 cable loading

Table 5-9. Intermediate-scale test 6

Time (s) Failure Observation

191 SOV-2 Fuse Clear – Negative

230 MOV-2 Fuse Clear – Negative

INTER-CABLE with SOV-2

850 SWGR-T SO [Breaker Open]

1168 SOV-2 Fuse Clear – Positive

1170 MOV-2 Fuse Clear – Positive

INTER-CABLE with SWGR-T conductor N2

1317 Lg Coil Fuse Clear – Positive and Negative

1400 – 1502 SOV-1 SO

1480 – 1507 MOV-1 SO Close Coil

1534 – 1567 Short between SOV-1 conductor G and SWGR-C conductor N1

1567 SOV-1 Fuse Clear – Positive and Negative

1548 – 1637 1-inch Valve SO

1603-1607 SWGR-C SO [Breaker Close]

1603-1607 SWGR-T SO [Breaker Open]

1638 1-inch Valve Fuse Clear – Negative

1728 SWGR-C and SWGR-T Fuse Clear – Negative

5.3.9 Test 7

No inter-cable hot shorts were identified in intermediate-scale test 7. Figure 5-19 and

Table 5-10 provide the cable loading configurations and summarize the circuit failure modes in

chronological order. Ground plane influences can be associated with the concurrent fuse

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

ac1-4 : SCDU circuits

M2 S2

SG-C

1V LC

SG-T

M1 S1

NOT TO SCALE

Inter-cable Circuit

5-20

clearing of MOV-1, MOV-2, and SOV-2 1286 seconds into the test. At this point, the battery

transitioned from being grounded on its positive side to being grounded on its negative side.

Figure 5-19. Intermediate-scale test 7 cable loading

Table 5-10. Intermediate-scale test 7

Time (s) Failure Observation

302 – 363 SOV-1 SO

324 MOV-1 Fuse Clear – Negative

363 SOV-1 Fuse Clear – Positive and Negative

466 SOV-2 Fuse Clear – Negative

535 MOV-2 Fuse Clear – Negative

1095 SWGR-T SO [Breaker Open]

1258 SWGR-C Fuse Clear – Negative

1286 MOV-1 Fuse Clear – Positive

1286 MOV-2 Fuse Clear – Negative

1286 SOV-2 Fuse Clear Positive

1388 SWGR-T Fuse Clear – Negative

1426 Lg Coil Fuse Clear – Negative

1713 – 1762 1-inch Valve SO

1762 1-inch Valve Fuse Clear – Negative

5.3.10 Test 8

Figure 5-20 shows the cable loading configuration for intermediate-scale test 8 while Table 5-11

contains the failure mode summary information, presented in chronological order. One intercable hot short was observed, which resulted in the spurious operation of MOV-1 close coil.

This short occurred when the G conductor of the large coil cable came into electrical contact

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

ac1-4 : SCDU circuits

M1 S1 LC

SG-C SG-T

1V

M2 S2

NOT TO SCALE Inter-cable Circuit

5-21

with close coil conductor YC1 of the MOV-1 circuit via a ground path. Figure 5-21 shows the

unbalanced current profiles for large coil and MOV-1. Note that these two cables were located

adjacent to each other in the same cable tray in location A, “flame exposure region.” Review of

the ground fault circuit data indicates that the positive side of the battery shorted to ground at

approximately 900 seconds and remained grounded for the duration of the test.

Figure 5-20. Intermediate-scale test 8 cable loading

Table 5-11. Intermediate-scale test 8

Time (s) Failure Observation

900 1-inch Valve Fuse Clear – Negative

943 – 1060 Lg Coil SO

960 – 1052 SOV-1 SO

1052 SOV-1 Fuse Clear – Positive and Negative

1052 – 1149 MOV-1 SO Close Coil

INTER-CABLE with Lg Coil conductor G via ground

1060 Lg Coil Fuse Clear – Negative

1149 MOV-1 Fuse Clear – Negative

1743 MOV-2 Fuse Clear – Negative

2354 SOV-2 Fuse Clear – Positive and Negative

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

ac1-4 : SCDU circuits

M2 S2

SG-C SG-T

NOT TO SCALE

Inter-cable Circuit

1V M1 S1 LC

ac1 ac2

ac3 ac4

5-22

Figure 5-21. Outstanding current shorting in intermediate-scale test 8, between MOV-1

and Lg Coil

5.3.11 Test 9

Figure 5-22 presents the cable loading configuration for intermediate-scale test 9, and Table 5-

12 provides the chronological order of the failure modes identified during this test. Three intercable spurious operations were observed during this test. MOV-2 open coil went through

spurious operation for 24 seconds via inter-cable shorting from conductors “G” and “P” of the

large coil circuit. Note that these two cables are set in different locations in the hood: MOV-2 is

in location D, while the large coil circuit is in the cable tray immediately below in Location B. At

1552 seconds into the test, the SOV-2 circuit experienced an inter-cable spurious operation

from the same source conductors as MOV-2 (namely conductors “G” and “P” from the large coil

circuit). This spurious operation lasted for 28 seconds. Again, both cables involved in the

shorting were set in different cable tray locations. The third and final inter-cable spurious

operation occurred when the MOV-1 close coil actuated after being energized by the switchgear

trip circuit. This spurious operation lasted for 16 seconds. In this case, the cables involved

were located in the same cable tray and were not adjacent to each other, but were separated by

a fill cable.

Time (s)

1000 1050 1100 1150 1200

Current (A)

-1.0

-0.5

0.0

0.5

1.0

1-inch Valve

Large Coil

MOV-1

MOV-2

SOV-1

SOV-2

Switchgear

5-23

Figure 5-22. Intermediate-scale test 9 cable loading

Table 5-12. Intermediate-scale test 9

Time (s) Failure Observation

628 – 638 1-inch Valve SA

765 Lg Coil Fuse Clear – Negative

765 1-inch Valve Fuse Clear – Positive and Negative

1253 – 1277 MOV-2 SO Open Coil

INTER-CABLE shorting with Lg Coil conductors G & P via ground

1278 MOV-2 Fuse Clear – Negative

1552 – 1580 SOV-2 SA

INTER-CABLE shorting with Lg Coil conductors G & P via ground

1583 SOV-2 Fuse Clear – Negative

1602 Lg Coil Fuse Clear – Positive – Short w/SWGR-T cond. N2 via ground

1604 SOV-2 Fuse Clear – Positive – Short w/SWGR-T cond. N2 via ground

1605 MOV-2 Fuse Clear – Positive – Short w/SWGR-T cond. N2 via ground

1920 SWGR-C Fuse Clear – Positive

2420 SWGR-C Fuse Clear – Negative – Short w/SOV-1 cond. P via ground

2584 – 2696 SOV-1 SO

2611 – 2627 MOV-1 SO Close Coil

INTER-CABLE shorting with SWGR-T conductor P via ground

2638 MOV-1 Fuse Clear – Negative

2699 SOV-1 Fuse Clear – Positive and Negative – Short w/SWGR-T cond. P

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

ac1-4 : SCDU circuits

NOT TO SCALE

Inter-cable Circuit

TC TC

1V

LC M1 S1

M2 S2 SG-C SG-T

5-24

5.3.12 Test 10

The cable configuration used in intermediate-scale test 10 is shown in Figure 5-23, and the

chronological order of the cable failures is presented in Table 5-13. The results show that there

were three spurious operations and one hot short as a result of ground fault equivalent shorting.

In all four instances, the source of the interactions could not be identified; however, this test

configuration has the inter-cable testing configuration in location A, directly above the fire. This

experimental set-up likely caused the inter-cable source conductors (which were not monitored

for current) to short to the ground plane and aid in the four cases of inter-cable shorting.

The first inter-cable spurious operation involved the MOV-2 close coil. It actuated at 2798s for

37 seconds, and the cable associated with this circuit was set in location B, directly above

location A, where the inter-cable test configuration was located. The second inter-cable

spurious operation occurred in location C and involved the MOV-1 open coil, which actuated at

3579s for 15 seconds.

Figure 5-23. Intermediate-scale test 10 cable loading

Table 5-13. Intermediate-scale test 10

Time (s) Failure Observation

2502 SOV-2 Fuse Clear – Negative

2635 – 2644 1-inch Valve SO

2646 1-inch Valve Fuse Clear – Positive and Negative

2798 – 2835 MOV-2 SO Close Coil

INTER-CABLE unknown source – likely inter-cable test circuit

2890 Lg Coil Fuse Clear – Positive and Negative

3108 SWGR-T SO [Breaker Open]

3177 SWGR-C Fuse Clear – Positive

3236 SWGR-C Fuse Clear – Negative

3579 – 3594 MOV-1 SO Open Coil

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

ac1-4 : SCDU circuits

1V

LC

NOT TO SCALE Inter-cable Circuit

S1

M1

TC TC TC

M2 SG-T/C S2

5-25

Table 5-13. Intermediate-scale test 10

Time (s) Failure Observation

INTER-CABLE unknown source – likely inter-cable test circuit

3594 – 3646 MOV-1 SO Close Coil

INTER-CABLE unknown source – likely inter-cable test circuit

3594 – 3605 MOV-1 HS Open Coil

INTER-CABLE unknown source – likely inter-cable test circuit

3646 SOV-2 Fuse Clear – Positive

3646 SOV-1 Fuse Clear – Positive and Negative

3646 MOV-1 Fuse Clear – Positive

The inter-cable interactions that occurred during intermediate-scale test #10 could not be linked

to any of the circuits that monitored current. Thus, these inter-cable interactions are likely a

result of interactions from the inter-cable circuit, which was not equipped with current-monitoring

transducers. These inter-cable interactions occurred in the MOV-2 and MOV-1 circuits.

5.3.13 Test 11

Intermediate-scale test 11 experienced one inter-cable ground equivalent hot short. Figure 5-24

illustrates the cable loading configuration for test 11, and Table 5-14 presents the chronological

fault mode sequence. The SOV-2 circuit went through spurious operation 2858s into the test,

and was powered by the “P” conductor of the large coil circuit. This interaction is shown in

Figure 5-25, where the large coil circuit is supplying power (positive current) and the SOV-2

circuit is absorbing power (negative current). The cables that are connected to this circuit are

located in different exposure locations; SOV-2 is in location D, directly above the large coil cable

in location B. The different locations and a review of the ground fault detection circuit response,

which shows that the battery positive shorted to ground at approximately 1440 seconds, indicate

that this inter-cable interaction is a result of ground equivalent hot shorting.

Figure 5-24. Intermediate-scale test 11 cable loading

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

ac1-4 : SCDU circuits

+/- : power source cable

NOT TO SCALE

Inter-cable Circuit

1V M1 S1 LC

M2 S2

ac1 ac3

+/-

ac2

5-26

Table 5-14. Intermediate-scale test 11

Time (s) Failure Observation

1179 – 1197 MOV-1 SO Open Coil

1182 – 1197 MOV-1 HS Close Coil

1197 MOV-1 Fuse Clear – Positive and Negative

1310 – 1312 1-inch Valve SO

1319 – 1323 1-inch Valve SO

1429 1-inch Valve Fuse Clear – Negative

1432 Lg Coil SO

1437 Lg Coil Fuse Clear – Negative

1569 SOV-1 Fuse Clear – Positive and Negative

2749 MOV-2 Fuse Clear – Negative – short with Lg Coil cond. P & G

2858 – 2917 SOV-2 SA

INTER-CABLE shorting from Lg Coil conductors P

2917 SOV-2 Fuse Clear – Negative

3351 MOV-2 Fuse Clear – Positive

3352 SOV-2 Fuse Clear – Positive

Figure 5-25. Intermediate-scale test 11 current summation

Time (s)

2840 2860 2880 2900 2920

Current (A)

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

1-inch Valve

Large Coil

MOV-1

MOV-2

SOV-1

SOV-2

5-27

5.3.14 Test 12

The cable loading configuration for this test is shown in Figure 5-26. Intermediate-scale test 12

experienced four inter-cable hot short-induced spurious operations. The source of the first two

spurious operations could not be identified, and, due to the location of the inter-cable test

configuration (location A), it is likely that the source came from this circuit. The other possible

source is a 35A +/- cable that was used to evaluate the response of the high-current

transducers. The current transducers did not pick up any current measurements; however, the

laboratory had difficulties getting these high-current transducers to function properly, so,

although it is unlikely that the 35A +/- cable was the source of the inter-cable interactions, the

lack of reliable data for the large 500A current transducers does not completely rule out the 35A

+/- cable. Fuses of the inter-cable circuit cleared at approximately 3125 seconds. After this

time, the remaining two inter-cable spurious operations occurred, and the source cables for

these interactions could be identified. The last piece of information that pointed to the intercable test cables being the source of the first two inter-cable spurious operations was that the

inter-cable test configuration was located in Location A, as was done in intermediate-scale test

10, which also experienced inter-cable shorting that could not identify the source cables. From

all of these observations, it is highly probable that the source cable for the first two inter-cable

shorting events is from the inter-cable test configuration in location A.

Figure 5-26. Intermediate-scale test 12 cable loading

Current summation plots are presented in Figure 5-27(a-d) for each of the inter-cable spurious

operations. As shown in Figure 5-27(a) and (b), there is no source current in these plots from

any of the surrogate circuits. Figure 5-27(c) and (d) show the source current from the 1-inch

and large coil circuits, respectively. It is interesting to note that in Figure 5-27(d), the large coil

cable is shorting via the ground to MOV-1 and 1-inch valve circuit, but no spurious operation

results.

Location C

Location B

Location D Location E

Location A

LEGEND

SG-T : Switchgear Trip

SG-C : Switchgear Close

S1 : SOV-1

S2 : SOV-2

M1: MOV-1

M2: MOV-2

LC : Large Coil

1V : 1-inch Valve

ac1-4 : SCDU circuits

+/- : power source cable 35A

M2 S2

M1

1V

NOT TO SCALE Inter-cable Circuit

ac1 ac2

LC

S1